onetaskgraph-github-projects 0.2.1

//! A stateless onetaskgraph source over one GitHub Projects v2 project.
//!
//! A project maps to the configured GitHub `ProjectV2`, not a repository: one Projects v2
//! board can contain work from several repositories and draft work from none. Project fields
//! read `ProjectV2.id`, `title`, `shortDescription`, `url`, `createdAt`, and `updatedAt`. Tasks
//! map from `ProjectV2Item.content` (`Issue`, `PullRequest`, or `DraftIssue`); labels read the
//! content's `labels` connection and `ProjectV2ItemFieldLabelValue`.
//!
//! Status reads the item value whose `ProjectV2ItemFieldSingleSelectValue.field.name` is
//! `Status`. Its option name is retained. The default maps Backlog, Todo/Open, In Progress/In
//! Review, Done/Closed/Merged, and Cancelled/Canceled; `status_mapping` overrides option names
//! case-insensitively, and all other user-defined names remain `Unknown`.
//!
//! `ProjectV2.items` pages but has no label, status, orphan, or content-search arguments.
//! Project listing alone is native; the plugin ignores every unsupported query predicate so the
//! engine can compensate from the wider result. Dependencies traverse underlying `Issue` nodes.
//! `Issue.blockedBy` supplies `DependsOn` edges and `Issue.blocking` supplies `DependedOnBy`
//! edges; pull requests and draft issues have neither field and therefore return an empty edge
//! page. Both dependency capabilities are `BothDirections`; project dependency reads aggregate
//! the configured project's issue edges. Projects v2 has no native project-to-project relationship,
//! so those aggregate edges use the related issues' `projectItems.project.id`.
//!
//! Writes update the configured board, create draft items (never another board), update existing
//! draft items, set the source-owned metadata field, and use GitHub's native issue dependency
//! mutation when both ends are issues. Required checks use only the local fixture server; the
//! ignored credentialed lane verifies the current schema, creates and reads back one uniquely
//! named draft, then deletes every matching project item and verifies that no residue remains.
#![deny(missing_docs)]

use std::collections::BTreeMap;

use chrono::{DateTime, Utc};
use onetaskgraph_plugin_api::{
    Capabilities, Cursor, DependencyEdge, DependencyEndpoint, DependencyKind, DependencySupport,
    Direction, Health, ItemKind, ItemWrite, Label, NativeId, Page, PageRequest, Project,
    ProjectQuery, Repository, SecretResolver, SourceError, SourceName, SourcePlugin, Status,
    StatusCategory, Support, Task, TaskQuery, TaskSource, WriteSupport,
};
use reqwest::{Client, StatusCode, Url};
use schemars::{Schema, schema_for};
use secrecy::{ExposeSecret, SecretString};
use serde::Deserialize;
use serde_json::{Value, json};

/// The registry name for this plugin.
pub const KIND: &str = "github-projects";
/// GitHub's maximum connection page size.
pub const MAX_PAGE_SIZE: u32 = 100;
/// Nested connection size which keeps GitHub's worst-case query below its node limit.
const NESTED_PAGE_SIZE: u32 = 50;

/// Exact GraphQL query documents issued by this plugin.
///
/// Keeping the production documents here lets the pinned-schema test validate the same bytes
/// that are sent to GitHub, rather than a test-only copy which could drift independently.
pub mod graphql {
    /// Reads the configured project and its task page.
    pub const PROJECT: &str = r#"query($owner:String!,$number:Int!,$first:Int!,$after:String,$nestedFirst:Int!){
      owner:repositoryOwner(login:$owner){
        ... on ProjectV2Owner{projectV2(number:$number){...Project}}
      }
    } fragment Project on ProjectV2 { id title shortDescription url createdAt updatedAt closed
      fields(first:$nestedFirst){nodes{
        ... on ProjectV2SingleSelectField{__typename id name options{id name}}
        ... on ProjectV2Field{__typename id name}
      }pageInfo{hasNextPage}}
      items(first:$first,after:$after){nodes{id fieldValues(first:$nestedFirst){nodes{
        ... on ProjectV2ItemFieldSingleSelectValue{name field{
          ... on ProjectV2SingleSelectField{id name options{id name}}
        }}
        ... on ProjectV2ItemFieldTextValue{text field{... on ProjectV2Field{id name}}}
        ... on ProjectV2ItemFieldLabelValue{labels(first:$nestedFirst){nodes{id name color}pageInfo{hasNextPage}}}
      }pageInfo{hasNextPage}} content{
        ... on Issue{__typename id title body url createdAt updatedAt state repository{nameWithOwner} labels(first:$nestedFirst){nodes{id name color}pageInfo{hasNextPage}}}
        ... on PullRequest{__typename id title body url createdAt updatedAt state repository{nameWithOwner} labels(first:$nestedFirst){nodes{id name color}pageInfo{hasNextPage}}}
        ... on DraftIssue{__typename id title body createdAt updatedAt}
      }} pageInfo{hasNextPage endCursor}}
    }"#;
    /// Reads both dependency directions for one issue.
    pub const TASK_DEPENDENCIES: &str = r#"query($id:ID!,$first:Int!,$after:String){node(id:$id){__typename ... on Issue{blockedBy(first:$first,after:$after){nodes{id}pageInfo{hasNextPage endCursor}}blocking(first:$first,after:$after){nodes{id}pageInfo{hasNextPage endCursor}}}}}"#;
    /// Continues the projects connection for an issue related to a dependency.
    pub const RELATED_PROJECTS: &str = r#"query($id:ID!,$first:Int!,$after:String!){node(id:$id){... on Issue{projectItems(first:$first,after:$after){nodes{project{id}}pageInfo{hasNextPage endCursor}}}}}"#;
    /// Reads issue dependencies and the projects containing each related issue.
    pub const PROJECT_DEPENDENCIES: &str = r#"query($id:ID!,$first:Int!,$after:String,$nestedFirst:Int!){node(id:$id){... on Issue{blockedBy(first:$first,after:$after){nodes{id projectItems(first:$nestedFirst){nodes{project{id}}pageInfo{hasNextPage endCursor}}}pageInfo{hasNextPage endCursor}}blocking(first:$first,after:$after){nodes{id projectItems(first:$nestedFirst){nodes{project{id}}pageInfo{hasNextPage endCursor}}}pageInfo{hasNextPage endCursor}}}}}"#;
    /// Creates a draft in the configured project.
    pub const CREATE_DRAFT: &str = r#"mutation($input:AddProjectV2DraftIssueInput!){addProjectV2DraftIssue(input:$input){projectItem{id content{... on DraftIssue{id}}}}}"#;
    /// Updates an existing draft's user-visible fields.
    pub const UPDATE_DRAFT: &str = r#"mutation($input:UpdateProjectV2DraftIssueInput!){updateProjectV2DraftIssue(input:$input){draftIssue{id}}}"#;
    /// Updates the visible fields of an issue-backed project item.
    pub const UPDATE_ISSUE: &str =
        r#"mutation($input:UpdateIssueInput!){updateIssue(input:$input){issue{id}}}"#;
    /// Updates a text or single-select value on one project item.
    pub const UPDATE_FIELD: &str = r#"mutation($input:UpdateProjectV2ItemFieldValueInput!){updateProjectV2ItemFieldValue(input:$input){projectV2Item{id}}}"#;
    /// Updates the one configured project; it never creates a board.
    pub const UPDATE_PROJECT: &str =
        r#"mutation($input:UpdateProjectV2Input!){updateProjectV2(input:$input){projectV2{id}}}"#;
    /// Adds GitHub's native issue blocked-by relationship.
    pub const ADD_BLOCKED_BY: &str = r#"mutation($input:AddBlockedByInput!){addBlockedBy(input:$input){issue{id} blockingIssue{id}}}"#;
    /// Removes one native issue blocked-by relationship.
    pub const REMOVE_BLOCKED_BY: &str = r#"mutation($input:RemoveBlockedByInput!){removeBlockedBy(input:$input){issue{id} blockingIssue{id}}}"#;
}

fn default_token_env() -> String {
    "GH_PROJECTS_TOKEN".to_owned()
}
fn default_endpoint() -> String {
    "https://api.github.com/graphql".to_owned()
}

/// Configuration for one GitHub Projects v2 project.
#[derive(Debug, Clone, Default, Deserialize, schemars::JsonSchema)]
#[serde(default, deny_unknown_fields)]
pub struct GitHubProjectsConfig {
    /// Login of the user or organization which owns the project.
    pub owner: String, // llmlint: ignore[invalid_states_unrepresentable] Schema DTO; `new` validates GitHub's owner grammar before private construction.
    /// The project number shown in its GitHub URL.
    pub project_number: u32, // llmlint: ignore[invalid_states_unrepresentable] Schema DTO; `new` bounds this to a positive GraphQL Int.
    /// Environment variable containing a fine-grained token with Projects and Issues read/write
    /// plus Pull requests read-only access for every repository represented on the board.
    #[serde(default = "default_token_env")]
    pub token_env: String, // llmlint: ignore[invalid_states_unrepresentable] Schema DTO; `new` validates the environment-variable grammar.
    /// GraphQL endpoint. GitHub Enterprise installations may override it.
    #[serde(default = "default_endpoint")]
    pub endpoint: String, // llmlint: ignore[invalid_states_unrepresentable] Schema DTO; `new` converts it to the private validated `Url`.
    /// Case-insensitive project status name to normalized category mapping.
    #[serde(default)]
    pub status_mapping: BTreeMap<String, StatusCategory>, // llmlint: ignore[invalid_states_unrepresentable] Schema DTO; normalization validates keys and converts them to `StatusName`.
}

/// Factory for [`GitHubProjectsSource`].
#[derive(Debug, Clone, Copy, Default)]
pub struct Plugin;

impl SourcePlugin for Plugin {
    fn kind(&self) -> &'static str {
        KIND
    }
    fn config_schema(&self) -> Schema {
        schema_for!(GitHubProjectsConfig)
    }
    fn build(
        &self,
        name: &SourceName,
        config: &Value,
        secrets: &dyn SecretResolver,
    ) -> Result<Box<dyn TaskSource>, SourceError> {
        let config: GitHubProjectsConfig =
            serde_json::from_value(config.clone()).map_err(|e| SourceError::Config {
                message: format!("source {name}: {e}"),
            })?;
        let source =
            GitHubProjectsSource::new(name, config, secrets).map_err(|error| match error {
                SourceError::Config { message } => SourceError::Config {
                    message: format!("source {name}: {message}"),
                },
                SourceError::Auth { message } => SourceError::Auth {
                    message: format!("source {name}: {message}"),
                },
                other => other,
            })?;
        Ok(Box::new(source))
    }
}

/// A source which reads GitHub afresh for every operation.
pub struct GitHubProjectsSource {
    /// This source's configured name, so a recorded far end naming it can be told from
    /// one naming a system this source knows nothing about.
    name: SourceName,
    owner: String, // llmlint: ignore[invalid_states_unrepresentable] Private, constructed only by `new` after full GitHub-owner validation.
    project_number: u32, // llmlint: ignore[invalid_states_unrepresentable] Private, constructed only by `new` after GraphQL-Int validation.
    endpoint: Url,
    token: SecretString,
    credential_name: String, // llmlint: ignore[invalid_states_unrepresentable] Private diagnostic value constructed only after environment-name validation.
    statuses: BTreeMap<StatusName, StatusCategory>,
    client: Client,
}

impl GitHubProjectsSource {
    /// Validate configuration and capture the named credential without exposing it.
    ///
    /// `name` is this source's configured name, kept for one comparison: a far end
    /// recorded as `<name>:<native>` is an item of this same source, which its own
    /// relationship was supposed to hold.
    pub fn new(
        name: &SourceName,
        config: GitHubProjectsConfig,
        secrets: &dyn SecretResolver,
    ) -> Result<Self, SourceError> {
        if !valid_github_owner(&config.owner) {
            return Err(SourceError::Config {
                message: "owner must be 1-39 ASCII letters, digits, or single hyphens, and cannot start or end with a hyphen".into(),
            });
        }
        if config.project_number == 0 || config.project_number > i32::MAX as u32 {
            return Err(SourceError::Config {
                message: format!("project_number must be between 1 and {}", i32::MAX),
            });
        }
        if !valid_environment_name(&config.token_env) {
            return Err(SourceError::Config {
                message: "token_env must be a valid environment-variable name".into(),
            });
        }
        let endpoint = Url::parse(&config.endpoint).map_err(|e| SourceError::Config {
            message: format!("endpoint is not a valid URL: {e}"),
        })?;
        if endpoint.scheme() != "https"
            && !(endpoint.scheme() == "http"
                && endpoint
                    .host_str()
                    .is_some_and(|h| h == "127.0.0.1" || h == "localhost" || h == "::1"))
        {
            return Err(SourceError::Config {
                message:
                    "endpoint must use HTTPS (HTTP is accepted only for a loopback test server)"
                        .into(),
            });
        }
        let token = secrets.get(&config.token_env).filter(|token| !token.expose_secret().trim().is_empty()).ok_or_else(|| SourceError::Auth {
            message: format!("environment variable {} is missing or empty; set it to a fine-grained GitHub token granting Projects and Issues read/write plus Pull requests read-only access for every repository represented on the board", config.token_env),
        })?;
        Ok(Self {
            name: name.clone(),
            owner: config.owner,
            project_number: config.project_number,
            endpoint,
            token,
            credential_name: config.token_env,
            statuses: normalize_status_mapping(config.status_mapping)?,
            client: Client::builder()
                .user_agent("onetaskgraph")
                .build()
                .map_err(|e| SourceError::Config {
                    message: format!("cannot build HTTP client: {e}"),
                })?,
        })
    }

    async fn graphql(&self, query: &str, variables: Value) -> Result<Value, SourceError> {
        let response = self
            .client
            .post(self.endpoint.clone())
            .bearer_auth(self.token.expose_secret())
            .json(&json!({"query": query, "variables": variables}))
            .send()
            .await
            .map_err(|e| SourceError::Unavailable {
                message: format!("GitHub GraphQL request failed: {e}"),
            })?;
        let status = response.status();
        let retry_after = response
            .headers()
            .get("retry-after")
            .and_then(|v| v.to_str().ok())
            .and_then(|v| v.parse().ok());
        let exhausted = response
            .headers()
            .get("x-ratelimit-remaining")
            .and_then(|v| v.to_str().ok())
            == Some("0");
        if status == StatusCode::TOO_MANY_REQUESTS || exhausted {
            return Err(SourceError::RateLimited {
                retry_after_seconds: retry_after,
            });
        }
        if status == StatusCode::UNAUTHORIZED || status == StatusCode::FORBIDDEN {
            return Err(SourceError::Auth {
                message: format!(
                    "GitHub rejected the configured credential with HTTP {status}; grant it Projects and Issues read/write plus Pull requests read-only access for every repository represented on the board"
                ),
            });
        }
        if !status.is_success() {
            return Err(SourceError::Unavailable {
                message: format!("GitHub GraphQL returned HTTP {status}"),
            });
        }
        let body: Value = response.json().await.map_err(|e| SourceError::Malformed {
            message: format!("GitHub returned invalid JSON: {e}"),
        })?;
        let errors = body
            .get("errors")
            .map(|value| {
                value.as_array().ok_or_else(|| SourceError::Malformed {
                    message: "GitHub response errors is not an array".into(),
                })
            })
            .transpose()?;
        if let Some(errors) = errors.filter(|errors| !errors.is_empty()) {
            let messages = errors
                .iter()
                .filter_map(|e| e.get("message").and_then(Value::as_str))
                .collect::<Vec<_>>()
                .join("; ");
            let message = if messages.is_empty() {
                "GitHub returned GraphQL errors".into()
            } else {
                messages
            };
            let normalized = message.to_ascii_lowercase();
            if normalized.contains("resource not accessible") || normalized.contains("scope") {
                return Err(SourceError::Auth {
                    message: format!(
                        "{message}; grant {} Projects and Issues read/write plus Pull requests read-only access for every repository represented on the board",
                        self.credential_name
                    ),
                });
            }
            return Err(SourceError::Refused { message });
        }
        body.get("data")
            .filter(|data| data.is_object())
            .cloned()
            .ok_or_else(|| SourceError::Malformed {
                message: "GitHub response has no data object".into(),
            })
    }

    // llmlint: ignore[boundary_inputs_validated] GitHub caps nested connections at 100 and
    // GraphQL cannot independently page them inside the outer item page. This source page is
    // deliberately bounded at that published maximum; the live drift journey exercises it.
    async fn project_value(
        &self,
        items_after: Option<&str>,
        items_first: u32,
    ) -> Result<Value, SourceError> {
        let data = self.graphql(graphql::PROJECT, json!({"owner":self.owner,"number":self.project_number,"first":items_first.min(MAX_PAGE_SIZE),"after":items_after,"nestedFirst":NESTED_PAGE_SIZE})).await?;
        let project = data
            .pointer("/owner/projectV2")
            .filter(|v| !v.is_null())
            .cloned()
            .ok_or_else(|| SourceError::Refused {
                message: format!(
                    "GitHub project {}/{} was not found or is not visible to the token",
                    self.owner, self.project_number
                ),
            })?;
        Ok(project)
    }

    fn status(&self, item: &Value) -> Result<Status, SourceError> {
        let fields = item
            .pointer("/fieldValues/nodes")
            .and_then(Value::as_array)
            .expect("task validates fieldValues.nodes before mapping status");
        let name = fields
            .iter()
            .find(|v| v.pointer("/field/name").and_then(Value::as_str) == Some("Status"))
            .map(|value| required_str(value, "name"))
            .transpose()?
            .or(optional_str(
                item.get("content").unwrap_or(&Value::Null),
                "state",
            )?)
            .unwrap_or("Unknown")
            .to_owned();
        let category = self
            .statuses
            .get(&StatusName::new(&name))
            .copied()
            .unwrap_or_else(|| match name.to_ascii_lowercase().as_str() {
                "backlog" => StatusCategory::Backlog,
                "todo" | "open" => StatusCategory::Todo,
                "in progress" | "in review" => StatusCategory::InProgress,
                "done" | "closed" | "merged" => StatusCategory::Done,
                "cancelled" | "canceled" => StatusCategory::Cancelled,
                _ => StatusCategory::Unknown,
            });
        Ok(Status { category, name })
    }

    fn labels(item: &Value) -> Result<Vec<Label>, SourceError> {
        let direct = optional_nodes(item.pointer("/content/labels"), "content labels")?;
        let field_values = item
            .pointer("/fieldValues/nodes")
            .and_then(Value::as_array)
            .expect("task validates fieldValues.nodes before mapping labels");
        let field = field_values
            .iter()
            .find_map(|value| value.get("labels"))
            .map(|labels| optional_nodes(Some(labels), "field labels"))
            .transpose()?
            .flatten();
        let labels = direct
            .into_iter()
            .flatten()
            .chain(field.into_iter().flatten())
            .map(|v| {
                Ok(Label {
                    id: NativeId(required_str(v, "id")?.to_owned()),
                    name: required_str(v, "name")?.to_owned(),
                    color: optional_str(v, "color")?.map(str::to_owned),
                })
            })
            .collect::<Result<Vec<_>, SourceError>>()?
            .into_iter()
            .fold(Vec::new(), |mut labels, label| {
                if !labels.iter().any(|x: &Label| x.id == label.id) {
                    labels.push(label);
                }
                labels
            });
        Ok(labels)
    }

    fn task(&self, project_id: &str, item: &Value) -> Result<Option<Task>, SourceError> {
        let content = item.get("content").ok_or_else(|| SourceError::Malformed {
            message: "GitHub project item is missing content".into(),
        })?;
        if content.is_null() {
            return Ok(None);
        }
        let field_values = item
            .get("fieldValues")
            .ok_or_else(|| SourceError::Malformed {
                message: "GitHub project item is missing fieldValues".into(),
            })?;
        complete_connection(field_values, "project item field values")?;
        field_values
            .get("nodes")
            .and_then(Value::as_array)
            .ok_or_else(|| SourceError::Malformed {
                message: "GitHub project item fieldValues.nodes is not an array".into(),
            })?;
        if let Some(labels) = content.get("labels") {
            complete_connection(labels, "content labels")?;
        }
        for field_value in field_values["nodes"].as_array().expect("validated above") {
            if let Some(labels) = field_value.get("labels") {
                complete_connection(labels, "project item field labels")?;
            }
        }
        Ok(Some(Task {
            id: NativeId(required_str(content, "id")?.to_owned()),
            title: required_str(content, "title")?.to_owned(),
            content: optional_str(content, "body")?
                .filter(|s| !s.is_empty())
                .map(str::to_owned),
            status: self.status(item)?,
            labels: Self::labels(item)?,
            project: Some(NativeId(project_id.to_owned())),
            url: optional_str(content, "url")?.map(str::to_owned),
            created_at: optional_time(content, "createdAt")?,
            updated_at: optional_time(content, "updatedAt")?,
            metadata: metadata_field(field_values)?,
            repositories: repositories(content, field_values)?,
        }))
    }

    fn project(&self, value: &Value) -> Result<Project, SourceError> {
        let id = required_str(value, "id")?;
        let (content, metadata) =
            metadata_description(optional_str(value, "shortDescription")?.map(str::to_owned))?;
        let repositories = repositories_from_metadata(&metadata)?;
        Ok(Project {
            id: NativeId(id.into()),
            title: required_str(value, "title")?.into(),
            content,
            status: Status {
                category: if required_bool(value, "closed")? {
                    StatusCategory::Done
                } else {
                    StatusCategory::InProgress
                },
                name: if required_bool(value, "closed")? {
                    "Closed"
                } else {
                    "Open"
                }
                .into(),
            },
            labels: vec![],
            url: optional_str(value, "url")?.map(str::to_owned),
            created_at: optional_time(value, "createdAt")?,
            updated_at: optional_time(value, "updatedAt")?,
            metadata,
            repositories,
        })
    }

    async fn all_tasks(&self) -> Result<Vec<Task>, SourceError> {
        let mut after = None;
        let mut tasks = Vec::new();
        loop {
            let project = self.project_value(after.as_deref(), MAX_PAGE_SIZE).await?;
            let project_id = required_str(&project, "id")?;
            let items = project
                .pointer("/items/nodes")
                .and_then(Value::as_array)
                .ok_or_else(|| SourceError::Malformed {
                    message: "GitHub project items.nodes is not an array".into(),
                })?;
            for item in items {
                if let Some(task) = self.task(project_id, item)? {
                    tasks.push(task);
                }
            }
            let page =
                project
                    .pointer("/items/pageInfo")
                    .ok_or_else(|| SourceError::Malformed {
                        message: "GitHub project items have no pageInfo".into(),
                    })?;
            if !required_bool(page, "hasNextPage")? {
                break;
            }
            let next = required_str(page, "endCursor")?;
            validate_cursor_progress(after.as_deref(), next)?;
            after = Some(next.to_owned());
        }
        Ok(tasks)
    }

    async fn board_and_item(
        &self,
        content_id: Option<&NativeId>,
    ) -> Result<(Value, Option<Value>), SourceError> {
        let mut after = None;
        loop {
            let project = self.project_value(after.as_deref(), MAX_PAGE_SIZE).await?;
            let nodes = project
                .pointer("/items/nodes")
                .and_then(Value::as_array)
                .ok_or_else(|| SourceError::Malformed {
                    message: "GitHub project items.nodes is not an array".into(),
                })?;
            let found = content_id.and_then(|wanted| {
                nodes
                    .iter()
                    .find(|item| {
                        item.pointer("/content/id").and_then(Value::as_str)
                            == Some(wanted.0.as_str())
                    })
                    .cloned()
            });
            if found.is_some() || content_id.is_none() {
                return Ok((project, found));
            }
            let page =
                project
                    .pointer("/items/pageInfo")
                    .ok_or_else(|| SourceError::Malformed {
                        message: "GitHub project items have no pageInfo".into(),
                    })?;
            if !required_bool(page, "hasNextPage")? {
                return Ok((project, None));
            }
            let next = required_str(page, "endCursor")?;
            validate_cursor_progress(after.as_deref(), next)?;
            after = Some(next.to_owned());
        }
    }

    async fn set_item_field(
        &self,
        project_id: &str,
        item_id: &str,
        field_id: &str,
        value: Value,
    ) -> Result<(), SourceError> {
        let data = self
            .graphql(
                graphql::UPDATE_FIELD,
                json!({"input":{
                    "projectId":project_id,"itemId":item_id,"fieldId":field_id,"value":value
                }}),
            )
            .await?;
        let returned = data
            .pointer("/updateProjectV2ItemFieldValue/projectV2Item")
            .ok_or_else(|| SourceError::Malformed {
                message: "GitHub field update returned no project item".into(),
            })?;
        if required_str(returned, "id")? != item_id {
            return Err(SourceError::Malformed {
                message: "GitHub field update returned the wrong project item".into(),
            });
        }
        Ok(())
    }

    async fn native_dependency_ids(&self, id: &NativeId) -> Result<Vec<String>, SourceError> {
        let mut after = None;
        let mut ids = Vec::new();
        loop {
            let data = self
                .graphql(
                    graphql::TASK_DEPENDENCIES,
                    json!({"id":id.0,"first":MAX_PAGE_SIZE,"after":after}),
                )
                .await?;
            let connection =
                data.pointer("/node/blockedBy")
                    .ok_or_else(|| SourceError::Malformed {
                        message: "GitHub dependency response has no blockedBy connection".into(),
                    })?;
            ids.extend(
                connection
                    .get("nodes")
                    .and_then(Value::as_array)
                    .ok_or_else(|| SourceError::Malformed {
                        message: "GitHub dependency response nodes is not an array".into(),
                    })?
                    .iter()
                    .map(|value| required_str(value, "id").map(str::to_owned))
                    .collect::<Result<Vec<_>, _>>()?,
            );
            let next = next_cursor(connection)?;
            if let Some(next) = &next {
                validate_cursor_progress(after.as_deref(), &next.0)?;
            }
            after = next.map(|cursor| cursor.0);
            if after.is_none() {
                return Ok(ids);
            }
        }
    }

    fn field<'a>(project: &'a Value, name: &str) -> Result<Option<&'a Value>, SourceError> {
        complete_connection(
            project.get("fields").unwrap_or(&Value::Null),
            "project fields",
        )?;
        let fields = project
            .pointer("/fields/nodes")
            .and_then(Value::as_array)
            .ok_or_else(|| SourceError::Malformed {
                message: "GitHub project fields.nodes is not an array".into(),
            })?;
        Ok(fields
            .iter()
            .find(|field| field.get("name").and_then(Value::as_str) == Some(name)))
    }

    fn task_metadata(
        write: &ItemWrite<Task>,
        repositories: RepositoryStorage,
    ) -> Result<BTreeMap<String, Value>, SourceError> {
        let mut metadata = write.item.metadata.clone();
        if repositories == RepositoryStorage::Recorded && !write.item.repositories.is_empty() {
            metadata.insert(
                Repository::METADATA_KEY.into(),
                Value::Array(
                    write
                        .item
                        .repositories
                        .iter()
                        .map(|repository| Value::String(repository.as_str().to_owned()))
                        .collect(),
                ),
            );
        } else {
            metadata.remove(Repository::METADATA_KEY);
        }
        if !write.depends_on.is_empty() {
            metadata.insert(
                DependencyEdge::RECORDED_KEY.into(),
                Value::Array(
                    write
                        .depends_on
                        .iter()
                        .map(|edge| endpoint_value(&edge.to))
                        .collect(),
                ),
            );
        } else {
            metadata.remove(DependencyEdge::RECORDED_KEY);
        }
        Ok(metadata)
    }

    async fn dependencies(
        &self,
        id: &NativeId,
        direction: Direction,
        page: &PageRequest,
    ) -> Result<Page<DependencyEdge>, SourceError> {
        validate_page(page)?;
        let limit = page.limit.min(MAX_PAGE_SIZE) as usize;
        let cursor = page.cursor.as_ref().map(|c| c.0.as_str());
        let recorded = recorded_offset(cursor, direction)?;
        // Asked for even in the recorded phase, whose page reads nothing from the
        // connection: `__typename` is what says whether this item has a native
        // relationship at all, and that is what decides which far ends the reserved key is
        // allowed to hold.
        let data = self
            .graphql(
                graphql::TASK_DEPENDENCIES,
                json!({"id":id.0,"first":page.limit.min(MAX_PAGE_SIZE),
                       "after":if recorded.is_some() {None} else {cursor}}),
            )
            .await?;
        let node =
            data.get("node")
                .filter(|v| !v.is_null())
                .ok_or_else(|| SourceError::Refused {
                    message: format!(
                        "GitHub item {} was not found or does not support dependencies",
                        id.0
                    ),
                })?;
        let connection_name = match direction {
            Direction::DependsOn => "blockedBy",
            Direction::DependedOnBy => "blocking",
        };
        // A draft or a pull request has neither `blockedBy` nor `blocking`, so nothing it
        // depends on can be named natively and the reserved key may hold any far end. An
        // issue's connections hold issues, so the key may not hold one of those.
        let natively_names =
            (required_str(node, "__typename")? == "Issue").then_some(ItemKind::Task);
        if let Some(offset) = recorded {
            return Ok(recorded_page(
                self.recorded_task_edges(id, direction, natively_names)
                    .await?,
                offset,
                limit,
            ));
        }
        if natively_names.is_none() {
            return Ok(recorded_page(
                self.recorded_task_edges(id, direction, natively_names)
                    .await?,
                0,
                limit,
            ));
        }
        let connection = node
            .get(connection_name)
            .ok_or_else(|| SourceError::Malformed {
                message: "GitHub dependency response is missing its connection".into(),
            })?;
        let nodes = connection
            .get("nodes")
            .and_then(Value::as_array)
            .ok_or_else(|| SourceError::Malformed {
                message: "GitHub dependency response nodes is not an array".into(),
            })?;
        // `from` depends on `to`, always. GitHub spells the same relationship from either
        // end — `blockedBy` lists what this item waits on, `blocking` lists what waits on
        // it — so the near item is `from` in one direction and `to` in the other.
        let items = nodes
            .iter()
            .map(|value| {
                let related = NativeId(required_str(value, "id")?.into());
                let (from, to) = match direction {
                    Direction::DependsOn => (id.clone(), related),
                    Direction::DependedOnBy => (related, id.clone()),
                };
                Ok(DependencyEdge {
                    from: DependencyEndpoint::from_native(from, ItemKind::Task),
                    to: DependencyEndpoint::from_native(to, ItemKind::Task),
                    kind: DependencyKind::Blocks,
                })
            })
            .collect::<Result<Vec<_>, SourceError>>()?;
        let mut next = next_cursor(connection)?;
        if let Some(next) = &next {
            validate_cursor_progress(cursor, &next.0)?;
        }
        if next.is_none()
            && !self
                .recorded_task_edges(id, direction, natively_names)
                .await?
                .is_empty()
        {
            next = Some(Cursor(format!("{RECORDED_CURSOR}0")));
        }
        Ok(Page { items, next })
    }

    /// The edges this item records under [`DependencyEdge::RECORDED_KEY`], which is where
    /// a far end in another source has to live: no GitHub issue relationship can name one.
    ///
    /// Only forwards. The reverse of a recorded edge is derived from the far end, and this
    /// source never writes one down.
    ///
    /// The metadata lives on the *project item*, not on the issue this method is given, so
    /// reading it costs one board scan. That is why it happens once the native connection
    /// is spent rather than on every page.
    async fn recorded_task_edges(
        &self,
        id: &NativeId,
        direction: Direction,
        natively_names: Option<ItemKind>,
    ) -> Result<Vec<DependencyEdge>, SourceError> {
        if direction != Direction::DependsOn {
            return Ok(Vec::new());
        }
        let Some(task) = self
            .all_tasks()
            .await?
            .into_iter()
            .find(|task| task.id == *id)
        else {
            return Ok(Vec::new());
        };
        DependencyEdge::recorded(
            &task.metadata,
            id,
            ItemKind::Task,
            &self.name,
            natively_names,
        )
        .map_err(|message| SourceError::Malformed { message })
    }

    async fn related_issue_projects(&self, issue: &Value) -> Result<Vec<NativeId>, SourceError> {
        let issue_id = required_str(issue, "id")?;
        let mut connection =
            issue
                .get("projectItems")
                .cloned()
                .ok_or_else(|| SourceError::Malformed {
                    message: "GitHub related issue is missing projectItems".into(),
                })?;
        let mut projects = Vec::new();
        let mut previous = None;
        loop {
            let nodes = connection
                .get("nodes")
                .and_then(Value::as_array)
                .ok_or_else(|| SourceError::Malformed {
                    message: "GitHub related issue projectItems.nodes is not an array".into(),
                })?;
            for item in nodes {
                projects.push(NativeId(
                    required_str(
                        item.get("project").ok_or_else(|| SourceError::Malformed {
                            message: "GitHub dependency project item has no project".into(),
                        })?,
                        "id",
                    )?
                    .into(),
                ));
            }
            let Some(cursor) = next_cursor(&connection)? else {
                break;
            };
            validate_cursor_progress(previous.as_deref(), &cursor.0)?;
            previous = Some(cursor.0.clone());
            let data = self
                .graphql(
                    graphql::RELATED_PROJECTS,
                    json!({"id":issue_id,"first":MAX_PAGE_SIZE,"after":cursor.0}),
                )
                .await?;
            connection = data.pointer("/node/projectItems").cloned().ok_or_else(|| {
                SourceError::Malformed {
                    message: "GitHub related issue response is missing projectItems".into(),
                }
            })?;
        }
        Ok(projects)
    }
}

#[derive(Clone, Copy, PartialEq, Eq)]
enum ContentKind {
    DraftIssue,
    Issue,
}
#[derive(Clone, Copy, PartialEq, Eq)]
enum RepositoryStorage {
    Native,
    Recorded,
}
impl ContentKind {
    fn parse(content: &Value) -> Result<Self, SourceError> {
        match required_str(content, "__typename")? {
            "DraftIssue" => Ok(Self::DraftIssue),
            "Issue" => Ok(Self::Issue),
            other => Err(SourceError::Refused {
                message: format!("GitHub {other} items cannot be updated by this destination"),
            }),
        }
    }
}

#[async_trait::async_trait]
impl TaskSource for GitHubProjectsSource {
    fn kind(&self) -> &'static str {
        KIND
    }
    fn capabilities(&self) -> Capabilities {
        Capabilities {
            projects: Support::Native,
            orphan_tasks: Support::Unsupported,
            filter_by_label: Support::Unsupported,
            filter_by_status: Support::Unsupported,
            search_title: Support::Unsupported,
            search_content: Support::Unsupported,
            task_dependencies: DependencySupport::BothDirections,
            project_dependencies: DependencySupport::BothDirections,
            max_page_size: MAX_PAGE_SIZE,
        }
    }
    async fn health(&self) -> Result<Health, SourceError> {
        let project = self.project_value(None, 1).await?;
        Ok(Health {
            reachable: true,
            detail: Some(format!(
                "reading GitHub project {}/{} ({})",
                self.owner,
                self.project_number,
                required_str(&project, "title")?
            )),
        })
    }
    async fn get_task(&self, id: &NativeId) -> Result<Option<Task>, SourceError> {
        Ok(self
            .all_tasks()
            .await?
            .into_iter()
            .find(|task| task.id == *id))
    }
    async fn get_project(&self, id: &NativeId) -> Result<Option<Project>, SourceError> {
        let value = self.project_value(None, 1).await?;
        let project = self.project(&value)?;
        Ok((project.id == *id).then_some(project))
    }
    async fn query_tasks(
        &self,
        _query: &TaskQuery,
        page: &PageRequest,
    ) -> Result<Page<Task>, SourceError> {
        validate_page(page)?;
        let value = self
            .project_value(page.cursor.as_ref().map(|c| c.0.as_str()), page.limit)
            .await?;
        let id = required_str(&value, "id")?;
        let items_connection = value.get("items").ok_or_else(|| SourceError::Malformed {
            message: "GitHub project response is missing items".into(),
        })?;
        let nodes = items_connection
            .get("nodes")
            .and_then(Value::as_array)
            .ok_or_else(|| SourceError::Malformed {
                message: "GitHub project items.nodes is not an array".into(),
            })?;
        let items = nodes
            .iter()
            .map(|item| self.task(id, item))
            .collect::<Result<Vec<_>, SourceError>>()?
            .into_iter()
            .flatten()
            .collect();
        let next = next_cursor(items_connection)?;
        if let Some(next) = &next {
            validate_cursor_progress(
                page.cursor.as_ref().map(|cursor| cursor.0.as_str()),
                &next.0,
            )?;
        }
        Ok(Page { items, next })
    }
    async fn query_projects(
        &self,
        _query: &ProjectQuery,
        page: &PageRequest,
    ) -> Result<Page<Project>, SourceError> {
        validate_page(page)?;
        if page.cursor.is_some() {
            return Err(SourceError::Config {
                message: "GitHub project listing does not issue page cursors".into(),
            });
        }
        Ok(Page::last(vec![
            self.project(&self.project_value(None, 1).await?)?,
        ]))
    }
    async fn labels(&self, page: &PageRequest) -> Result<Page<Label>, SourceError> {
        validate_page(page)?;
        let offset = numeric_cursor(page.cursor.as_ref())?;
        let mut labels = self
            .all_tasks()
            .await?
            .into_iter()
            .flat_map(|t| t.labels)
            .fold(Vec::new(), |mut all, label| {
                if !all.iter().any(|x: &Label| x.id == label.id) {
                    all.push(label);
                }
                all
            });
        labels.sort_by(|a, b| a.name.cmp(&b.name).then(a.id.0.cmp(&b.id.0)));
        Ok(offset_page(
            labels,
            offset,
            page.limit.min(MAX_PAGE_SIZE) as usize,
        ))
    }
    async fn task_dependencies(
        &self,
        id: &NativeId,
        direction: Direction,
        page: &PageRequest,
    ) -> Result<Page<DependencyEdge>, SourceError> {
        self.dependencies(id, direction, page).await
    }
    async fn project_dependencies(
        &self,
        id: &NativeId,
        direction: Direction,
        page: &PageRequest,
    ) -> Result<Page<DependencyEdge>, SourceError> {
        validate_page(page)?;
        let project = self.project_value(None, 1).await?;
        if required_str(&project, "id")? != id.0 {
            return Err(SourceError::Refused {
                message: format!("GitHub project {} was not found", id.0),
            });
        }
        let mut edges = Vec::new();
        for task in self.all_tasks().await? {
            let mut cursor = None;
            loop {
                let data = self.graphql(graphql::PROJECT_DEPENDENCIES, json!({"id":task.id.0,"first":MAX_PAGE_SIZE,"after":cursor.as_ref().map(|cursor: &Cursor| cursor.0.as_str()),"nestedFirst":MAX_PAGE_SIZE})).await?;
                let connection_name = match direction {
                    Direction::DependsOn => "blockedBy",
                    Direction::DependedOnBy => "blocking",
                };
                let Some(connection) = data.pointer(&format!("/node/{connection_name}")) else {
                    // Pull requests and draft issues are valid project tasks, but the inline
                    // `... on Issue` selection intentionally yields no dependency connection.
                    break;
                };
                let related_issues = connection
                    .get("nodes")
                    .and_then(Value::as_array)
                    .ok_or_else(|| SourceError::Malformed {
                        message: "GitHub project dependency nodes is not an array".into(),
                    })?;
                for related_issue in related_issues {
                    for related in self.related_issue_projects(related_issue).await? {
                        if related != *id {
                            // Same orientation as the task level above, one level up.
                            let (from, to) = match direction {
                                Direction::DependsOn => (id.clone(), related),
                                Direction::DependedOnBy => (related, id.clone()),
                            };
                            edges.push(DependencyEdge {
                                from: DependencyEndpoint::from_native(from, ItemKind::Project),
                                to: DependencyEndpoint::from_native(to, ItemKind::Project),
                                kind: DependencyKind::Blocks,
                            });
                        }
                    }
                }
                let next = next_cursor(connection)?;
                if let Some(next) = &next {
                    validate_cursor_progress(
                        cursor.as_ref().map(|value: &Cursor| value.0.as_str()),
                        &next.0,
                    )?;
                }
                cursor = next;
                if cursor.is_none() {
                    break;
                }
            }
        }
        if direction == Direction::DependsOn {
            // A board's edges are aggregated from its issues, so another board is exactly
            // what this source can relate it to — and exactly what the reserved key must
            // not hold.
            edges.extend(
                DependencyEdge::recorded(
                    &self.project(&project)?.metadata,
                    id,
                    ItemKind::Project,
                    &self.name,
                    Some(ItemKind::Project),
                )
                .map_err(|message| SourceError::Malformed { message })?,
            );
        }
        let offset = numeric_cursor(page.cursor.as_ref())?;
        Ok(offset_page(edges, offset, page.limit as usize))
    }

    fn writes(&self) -> WriteSupport {
        WriteSupport::Supported
    }

    async fn write_task(&self, write: &ItemWrite<Task>) -> Result<NativeId, SourceError> {
        let (project, existing) = self.board_and_item(write.target.as_ref()).await?;
        let project_id = required_str(&project, "id")?;
        let metadata_field =
            Self::field(&project, METADATA_FIELD)?.ok_or_else(|| SourceError::Refused {
                message: format!("GitHub project has no source-owned {METADATA_FIELD} text field"),
            })?;
        if required_str(metadata_field, "__typename")? != "ProjectV2Field" {
            return Err(SourceError::Refused {
                message: format!(
                    "GitHub project source-owned {METADATA_FIELD} field is not a text field"
                ),
            });
        }
        let status_selection =
            Some(
                Self::field(&project, "Status")?.ok_or_else(|| SourceError::Refused {
                    message: "GitHub project has no Status field".into(),
                })?,
            )
            .map(|field| {
                if required_str(field, "__typename")? != "ProjectV2SingleSelectField" {
                    return Err(SourceError::Refused {
                        message: "GitHub project Status field is not a single-select field".into(),
                    });
                }
                let option = field
                    .get("options")
                    .and_then(Value::as_array)
                    .and_then(|options| {
                        options.iter().find(|option| {
                            option
                                .get("name")
                                .and_then(Value::as_str)
                                .is_some_and(|name| {
                                    name.eq_ignore_ascii_case(&write.item.status.name)
                                })
                        })
                    })
                    .ok_or_else(|| SourceError::Refused {
                        message: format!(
                            "GitHub Status field cannot represent status {}",
                            write.item.status.name
                        ),
                    })?;
                Ok::<_, SourceError>((
                    required_str(field, "id")?.to_owned(),
                    required_str(option, "id")?.to_owned(),
                ))
            })
            .transpose()?;
        let (content_id, item_id, content_kind) = if let Some(target) = &write.target {
            let item = existing.ok_or_else(|| SourceError::Refused {
                message: format!("GitHub destination item {} was not found", target.0),
            })?;
            let content_kind = ContentKind::parse(item.get("content").unwrap_or(&Value::Null))?;
            if content_kind == ContentKind::DraftIssue && !write.item.labels.is_empty() {
                return Err(SourceError::Refused {
                    message: "GitHub draft items cannot represent labels".into(),
                });
            }
            if content_kind == ContentKind::Issue {
                let held = Self::labels(&item)?;
                if held != write.item.labels {
                    return Err(SourceError::Refused {
                        message: "GitHub issue labels differ from the labels being written".into(),
                    });
                }
                let native = item
                    .pointer("/content/repository/nameWithOwner")
                    .and_then(Value::as_str)
                    .map(|value| format!("github.com/{value}"));
                if write
                    .item
                    .repositories
                    .iter()
                    .map(Repository::as_str)
                    .collect::<Vec<_>>()
                    != native.iter().map(String::as_str).collect::<Vec<_>>()
                {
                    return Err(SourceError::Refused {
                        message:
                            "GitHub issue repository differs from the repositories being written"
                                .into(),
                    });
                }
            }
            let operation = match content_kind {
                ContentKind::DraftIssue => graphql::UPDATE_DRAFT,
                ContentKind::Issue => graphql::UPDATE_ISSUE,
            };
            let input = if content_kind == ContentKind::DraftIssue {
                json!({"draftIssueId":target.0,"title":write.item.title,"body":write.item.content})
            } else {
                json!({"id":target.0,"title":write.item.title,"body":write.item.content})
            };
            let data = self.graphql(operation, json!({"input":input})).await?;
            let pointer = if content_kind == ContentKind::DraftIssue {
                "/updateProjectV2DraftIssue/draftIssue"
            } else {
                "/updateIssue/issue"
            };
            let returned = data
                .pointer(pointer)
                .ok_or_else(|| SourceError::Malformed {
                    message: "GitHub item update returned no item".into(),
                })?;
            if required_str(returned, "id")? != target.0 {
                return Err(SourceError::Malformed {
                    message: "GitHub item update returned the wrong item".into(),
                });
            }
            (
                target.clone(),
                NativeId(required_str(&item, "id")?.into()),
                content_kind,
            )
        } else {
            if !write.item.labels.is_empty() {
                return Err(SourceError::Refused {
                    message: "GitHub draft items cannot represent labels".into(),
                });
            }
            let data = self
                .graphql(
                    graphql::CREATE_DRAFT,
                    json!({"input":{
                        "projectId":project_id,"title":write.item.title,"body":write.item.content
                    }}),
                )
                .await?;
            let created = data
                .pointer("/addProjectV2DraftIssue/projectItem")
                .ok_or_else(|| SourceError::Malformed {
                    message: "GitHub draft creation returned no project item".into(),
                })?;
            (
                NativeId(
                    required_str(created.pointer("/content").unwrap_or(&Value::Null), "id")?.into(),
                ),
                NativeId(required_str(created, "id")?.into()),
                ContentKind::DraftIssue,
            )
        };

        let mut fallback = Vec::new();
        let mut native = Vec::new();
        for edge in &write.depends_on {
            let same_source = edge
                .to
                .source()
                .is_none_or(|source| source == self.name.as_str());
            let far_id = edge
                .to
                .id()
                .rsplit_once(':')
                .map_or(edge.to.id(), |(_, id)| id);
            let far_issue = if same_source {
                let far = self
                    .board_and_item(Some(&NativeId(far_id.into())))
                    .await?
                    .1
                    .ok_or_else(|| SourceError::Refused {
                        message: format!("GitHub dependency item {far_id} was not found"),
                    })?;
                match required_str(far.get("content").unwrap_or(&Value::Null), "__typename")? {
                    "Issue" => true,
                    "DraftIssue" | "PullRequest" => false,
                    other => {
                        return Err(SourceError::Malformed {
                            message: format!(
                                "GitHub dependency item has unknown content type {other}"
                            ),
                        });
                    }
                }
            } else {
                false
            };
            if content_kind == ContentKind::Issue && far_issue && edge.to.kind == ItemKind::Task {
                native.push(far_id.to_owned());
            } else {
                fallback.push(edge.clone());
            }
        }
        if content_kind == ContentKind::Issue {
            let current = self.native_dependency_ids(&content_id).await?;
            for (operation, far_id) in current
                .iter()
                .filter(|id| !native.contains(id))
                .map(|id| (graphql::REMOVE_BLOCKED_BY, id))
                .chain(
                    native
                        .iter()
                        .filter(|id| !current.contains(id))
                        .map(|id| (graphql::ADD_BLOCKED_BY, id)),
                )
            {
                let data = self
                    .graphql(
                        operation,
                        json!({"input":{"issueId":content_id.0,"blockingIssueId":far_id}}),
                    )
                    .await?;
                let root = if operation == graphql::ADD_BLOCKED_BY {
                    "addBlockedBy"
                } else {
                    "removeBlockedBy"
                };
                let issue = data.pointer(&format!("/{root}/issue")).ok_or_else(|| {
                    SourceError::Malformed {
                        message: "GitHub dependency update returned no issue".into(),
                    }
                })?;
                let blocker = data
                    .pointer(&format!("/{root}/blockingIssue"))
                    .ok_or_else(|| SourceError::Malformed {
                        message: "GitHub dependency update returned no blocking issue".into(),
                    })?;
                if required_str(issue, "id")? != content_id.0
                    || required_str(blocker, "id")? != far_id
                {
                    return Err(SourceError::Malformed {
                        message: "GitHub dependency update returned the wrong issues".into(),
                    });
                }
            }
        }
        let metadata_write = ItemWrite {
            target: write.target.clone(),
            item: write.item.clone(),
            depends_on: fallback,
        };
        let storage = if content_kind == ContentKind::Issue {
            RepositoryStorage::Native
        } else {
            RepositoryStorage::Recorded
        };
        let metadata = Self::task_metadata(&metadata_write, storage)?;
        self.set_item_field(
            project_id,
            &item_id.0,
            required_str(metadata_field, "id")?,
            json!({"text":Value::Object(metadata.clone().into_iter().collect()).to_string()}),
        )
        .await?;

        if let Some((field_id, option_id)) = status_selection {
            self.set_item_field(
                project_id,
                &item_id.0,
                &field_id,
                json!({"singleSelectOptionId":option_id}),
            )
            .await?;
        }
        Ok(content_id)
    }

    async fn write_project(&self, write: &ItemWrite<Project>) -> Result<NativeId, SourceError> {
        let project = self.project_value(None, 1).await?;
        let id = NativeId(required_str(&project, "id")?.into());
        if write.target.as_ref().is_some_and(|target| target != &id) {
            return Err(SourceError::Refused {
                message: format!(
                    "GitHub project {} was not found",
                    write.target.as_ref().unwrap().0
                ),
            });
        }
        if !write.item.labels.is_empty() {
            return Err(SourceError::Refused {
                message: "GitHub Projects v2 cannot represent project labels".into(),
            });
        }
        let mut metadata = write.item.metadata.clone();
        metadata.insert(
            Repository::METADATA_KEY.into(),
            Value::Array(
                write
                    .item
                    .repositories
                    .iter()
                    .map(|repository| Value::String(repository.as_str().to_owned()))
                    .collect(),
            ),
        );
        metadata.insert(
            DependencyEdge::RECORDED_KEY.into(),
            Value::Array(
                write
                    .depends_on
                    .iter()
                    .map(|edge| endpoint_value(&edge.to))
                    .collect(),
            ),
        );
        let description = project_metadata_description(write.item.content.as_deref(), &metadata)?;
        let data = self
            .graphql(
                graphql::UPDATE_PROJECT,
                json!({"input":{
                    "projectId":id.0,"title":write.item.title,"shortDescription":description,
                    "closed":write.item.status.category == StatusCategory::Done
                }}),
            )
            .await?;
        let returned =
            data.pointer("/updateProjectV2/projectV2")
                .ok_or_else(|| SourceError::Malformed {
                    message: "GitHub project update returned no project".into(),
                })?;
        if required_str(returned, "id")? != id.0 {
            return Err(SourceError::Malformed {
                message: "GitHub project update returned the wrong project".into(),
            });
        }
        Ok(id)
    }
}

/// Where the recorded tail of a task-dependency walk resumes; see
/// [`GitHubProjectsSource::recorded_task_edges`].
const RECORDED_CURSOR: &str = "onetaskgraph.depends_on:";

/// Where a recorded tail resumes, refusing a cursor no walk in `direction` reported.
///
/// The reserved key holds forward edges and nothing else — the reverse of a recorded edge
/// is derived from the far end, never written down on the near item — so only a forward
/// walk ever reports one of these cursors. A reverse read carrying one is resuming a walk
/// it did not come from, and it is told so rather than answered with an empty page that
/// reads as a walk which ended.
fn recorded_offset(
    cursor: Option<&str>,
    direction: Direction,
) -> Result<Option<usize>, SourceError> {
    cursor
        .and_then(|cursor| cursor.strip_prefix(RECORDED_CURSOR))
        .map(|offset| {
            if direction != Direction::DependsOn {
                return Err(SourceError::Config {
                    message: format!(
                        "{RECORDED_CURSOR}{offset} resumes recorded forward edges, which a \
                         reverse dependency read never issues; resume it in the direction \
                         that reported it"
                    ),
                });
            }
            offset.parse().map_err(|_| SourceError::Config {
                message: format!("{RECORDED_CURSOR}{offset} is not a recorded-edge cursor"),
            })
        })
        .transpose()
}

fn recorded_page(edges: Vec<DependencyEdge>, offset: usize, limit: usize) -> Page<DependencyEdge> {
    let mut page = offset_page(edges, offset, limit.max(1));
    page.next = page
        .next
        .map(|cursor| Cursor(format!("{RECORDED_CURSOR}{}", cursor.0)));
    page
}

fn normalize_status_mapping(
    mapping: BTreeMap<String, StatusCategory>,
) -> Result<BTreeMap<StatusName, StatusCategory>, SourceError> {
    let mut normalized = BTreeMap::new();
    for (name, category) in mapping {
        if name.trim().is_empty() {
            return Err(SourceError::Config {
                message: "status_mapping contains a blank status name".into(),
            });
        }
        let key = StatusName::new(&name);
        if normalized.insert(key, category).is_some() {
            return Err(SourceError::Config {
                message: format!("status_mapping contains case-insensitive duplicate {name}"),
            });
        }
    }
    Ok(normalized)
}

fn valid_github_owner(owner: &str) -> bool {
    !owner.is_empty()
        && owner.len() <= 39
        && !owner.starts_with('-')
        && !owner.ends_with('-')
        && !owner.contains("--")
        && owner
            .bytes()
            .all(|byte| byte.is_ascii_alphanumeric() || byte == b'-')
}

fn valid_environment_name(name: &str) -> bool {
    let mut bytes = name.bytes();
    bytes
        .next()
        .is_some_and(|byte| byte.is_ascii_alphabetic() || byte == b'_')
        && bytes.all(|byte| byte.is_ascii_alphanumeric() || byte == b'_')
}

#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct StatusName(String);

impl StatusName {
    fn new(name: &str) -> Self {
        Self(name.to_lowercase())
    }
}

fn required_str<'a>(value: &'a Value, field: &str) -> Result<&'a str, SourceError> {
    value
        .get(field)
        .and_then(Value::as_str)
        .ok_or_else(|| SourceError::Malformed {
            message: format!("GitHub response is missing string field {field}"),
        })
}

const METADATA_FIELD: &str = "onetaskgraph.metadata";

fn endpoint_value(endpoint: &DependencyEndpoint) -> Value {
    json!({"id":endpoint.id(), "kind":match endpoint.kind { ItemKind::Task => "task", ItemKind::Project => "project" }})
}

fn metadata_field(field_values: &Value) -> Result<BTreeMap<String, Value>, SourceError> {
    let nodes = field_values
        .get("nodes")
        .and_then(Value::as_array)
        .ok_or_else(|| SourceError::Malformed {
            message: "GitHub project item fieldValues.nodes is not an array".into(),
        })?;
    let Some(text) = nodes
        .iter()
        .find(|node| node.pointer("/field/name").and_then(Value::as_str) == Some(METADATA_FIELD))
        .and_then(|node| node.get("text"))
    else {
        return Ok(BTreeMap::new());
    };
    text.as_str()
        .ok_or_else(|| SourceError::Malformed {
            message: format!("GitHub {METADATA_FIELD} field text is not a string"),
        })
        .and_then(|text| {
            serde_json::from_str(text).map_err(|error| SourceError::Malformed {
                message: format!(
                    "GitHub {METADATA_FIELD} field is not canonical JSON metadata: {error}"
                ),
            })
        })
}

fn repositories(content: &Value, field_values: &Value) -> Result<Vec<Repository>, SourceError> {
    if let Some(origin) = content
        .pointer("/repository/nameWithOwner")
        .and_then(Value::as_str)
    {
        return Repository::try_from(format!("github.com/{origin}"))
            .map(|repository| vec![repository])
            .map_err(|message| SourceError::Malformed { message });
    }
    repositories_from_metadata(&metadata_field(field_values)?)
}

const PROJECT_METADATA_OPEN: &str = "<!-- onetaskgraph.metadata\n";
const PROJECT_METADATA_CLOSE: &str = "\n-->";

fn metadata_description(
    description: Option<String>,
) -> Result<(Option<String>, BTreeMap<String, Value>), SourceError> {
    let Some(description) = description else {
        return Ok((None, BTreeMap::new()));
    };
    let Some(start) = description.rfind(PROJECT_METADATA_OPEN) else {
        return Ok((Some(description), BTreeMap::new()));
    };
    let value_start = start + PROJECT_METADATA_OPEN.len();
    let Some(relative_end) = description[value_start..].find(PROJECT_METADATA_CLOSE) else {
        return Err(SourceError::Malformed {
            message: "unterminated onetaskgraph metadata slot in GitHub project description".into(),
        });
    };
    let value_end = value_start + relative_end;
    if !description[value_end + PROJECT_METADATA_CLOSE.len()..]
        .trim()
        .is_empty()
    {
        return Ok((Some(description), BTreeMap::new()));
    }
    let metadata = serde_json::from_str(&description[value_start..value_end]).map_err(|error| {
        SourceError::Malformed {
            message: format!("invalid canonical JSON in GitHub project metadata slot: {error}"),
        }
    })?;
    let visible = description[..start].trim_end();
    Ok(((!visible.is_empty()).then(|| visible.into()), metadata))
}

fn project_metadata_description(
    content: Option<&str>,
    metadata: &BTreeMap<String, Value>,
) -> Result<Option<String>, SourceError> {
    if metadata.is_empty() {
        return Ok(content.filter(|value| !value.is_empty()).map(str::to_owned));
    }
    let encoded = Value::Object(metadata.clone().into_iter().collect()).to_string();
    Ok(Some(format!(
        "{}{}{}\n{}",
        content.unwrap_or_default(),
        if content.is_some_and(|value| !value.is_empty()) {
            "\n\n"
        } else {
            ""
        },
        PROJECT_METADATA_OPEN,
        format_args!("{encoded}\n-->")
    )))
}

fn repositories_from_metadata(
    metadata: &BTreeMap<String, Value>,
) -> Result<Vec<Repository>, SourceError> {
    Repository::from_metadata(metadata).map_err(|message| SourceError::Malformed { message })
}
fn required_bool(value: &Value, field: &str) -> Result<bool, SourceError> {
    value
        .get(field)
        .and_then(Value::as_bool)
        .ok_or_else(|| SourceError::Malformed {
            message: format!("GitHub response is missing boolean field {field}"),
        })
}
fn optional_str<'a>(value: &'a Value, field: &str) -> Result<Option<&'a str>, SourceError> {
    match value.get(field) {
        None | Some(Value::Null) => Ok(None),
        Some(value) => value
            .as_str()
            .map(Some)
            .ok_or_else(|| SourceError::Malformed {
                message: format!("GitHub response field {field} is not a string or null"),
            }),
    }
}
fn optional_nodes<'a>(
    connection: Option<&'a Value>,
    name: &str,
) -> Result<Option<&'a Vec<Value>>, SourceError> {
    match connection {
        None | Some(Value::Null) => Ok(None),
        Some(value) => value
            .get("nodes")
            .and_then(Value::as_array)
            .map(Some)
            .ok_or_else(|| SourceError::Malformed {
                message: format!("GitHub {name}.nodes is not an array"),
            }),
    }
}
fn complete_connection(connection: &Value, name: &str) -> Result<(), SourceError> {
    let page_info = connection
        .get("pageInfo")
        .ok_or_else(|| SourceError::Malformed {
            message: format!("GitHub {name} has no pageInfo"),
        })?;
    if required_bool(page_info, "hasNextPage")? {
        return Err(SourceError::Malformed {
            message: format!(
                "GitHub {name} exceeds the supported nested connection size of {NESTED_PAGE_SIZE}"
            ),
        });
    }
    Ok(())
}
fn optional_time(value: &Value, field: &str) -> Result<Option<DateTime<Utc>>, SourceError> {
    optional_str(value, field)?
        .map(|timestamp| {
            timestamp.parse().map_err(|error| SourceError::Malformed {
                message: format!("GitHub response field {field} is not a timestamp: {error}"),
            })
        })
        .transpose()
}
fn validate_page(page: &PageRequest) -> Result<(), SourceError> {
    if page.limit == 0 {
        Err(SourceError::Config {
            message: "page limit must be at least 1".into(),
        })
    } else {
        Ok(())
    }
}
fn next_cursor(connection: &Value) -> Result<Option<Cursor>, SourceError> {
    let page = connection
        .get("pageInfo")
        .filter(|value| value.is_object())
        .ok_or_else(|| SourceError::Malformed {
            message: "GitHub connection is missing pageInfo".into(),
        })?;
    if required_bool(page, "hasNextPage")? {
        let cursor = required_str(page, "endCursor")?;
        validate_cursor_progress(None, cursor)?;
        Ok(Some(Cursor(cursor.into())))
    } else {
        Ok(None)
    }
}
fn validate_cursor_progress(previous: Option<&str>, next: &str) -> Result<(), SourceError> {
    if next.is_empty() || previous == Some(next) {
        Err(SourceError::Malformed {
            message: "GitHub pagination cursor is empty or did not advance".into(),
        })
    } else {
        Ok(())
    }
}
fn numeric_cursor(cursor: Option<&Cursor>) -> Result<usize, SourceError> {
    cursor.map_or(Ok(0), |c| {
        c.0.parse().map_err(|_| SourceError::Config {
            message: "label cursor is invalid".into(),
        })
    })
}
fn offset_page<T>(mut items: Vec<T>, offset: usize, limit: usize) -> Page<T> {
    if offset > items.len() {
        return Page::last(vec![]);
    }
    let tail = items.split_off(offset);
    let mut selected = tail;
    let next = (selected.len() > limit).then(|| Cursor((offset + limit).to_string()));
    selected.truncate(limit);
    Page {
        items: selected,
        next,
    }
}