aion_package/

hash.rs

//! Content-hash computation over the canonical beam set.

use std::{fmt, str::FromStr, time::Duration};

use serde::{Deserialize, Deserializer, Serialize, Serializer, de};
use sha2::{Digest, Sha256};

use crate::{BeamSet, Manifest, PackageContract, PackageError};

const DIGEST_LEN: usize = 32;
const TEXT_LEN: usize = DIGEST_LEN * 2;
const WORKFLOW_TIMEOUT_DOMAIN: &[u8] = b"aion.package.version.workflow-timeout.v1";
const WORKFLOW_TIMEOUTS_DOMAIN: &[u8] = b"aion.package.version.workflow-timeouts.v3";
// `.v5` because `ActionContract` records now always end with a declarative
// body block. The `.v4` domain's records ended with an OPTIONAL advisory
// marker — its one injective tail-append — so the body block required a new
// domain rather than a second conditional suffix. Archives hashed under
// `.v4` refuse to load and must be redeployed; this build carries no
// compatibility shims by policy.
const WORKER_CONTRACT_DOMAIN: &[u8] = b"aion.package.version.worker-contract.v5";

/// A SHA-256 package version identity.
///
/// Legacy identities cover each module's logical name and exact `.beam` bytes
/// in [`BeamSet`] canonical order. Explicit-timeout identities append a
/// domain-separated timeout encoding. Archive representation and optional
/// source inclusion never participate, so deterministic inputs keep one version.
///
/// "Source inclusion" is EVERY archived-source family, and this is a declared
/// non-property rather than an accident of the current encoding: neither the
/// Gleam `src/` entries nor the AWL `awl/document/` + `awl/schema/` entries
/// (see [`crate::awl`]) contribute a byte to any identity above. Two packages
/// that differ ONLY in whether they carry an authored AWL document, or in what
/// that document says, are the SAME version — the provenance an archive shows
/// is declared unbound from identity, never ambiently assumed to be bound.
/// Pinned by `source_inclusion_does_not_change_manifest_version` and
/// `awl_source_inclusion_does_not_change_manifest_version` in
/// [`crate::builder`].
///
/// Its stable textual form is 64 lowercase hexadecimal characters. That text is
/// the package version identifier stored in the manifest and the hash component
/// embedded in namespaced deployed module names; it contains only `0-9a-f`,
/// which is safe for a BEAM module-name component.
#[derive(Clone, Debug, PartialEq, Eq, Hash)]
pub struct ContentHash([u8; DIGEST_LEN]);

impl ContentHash {
    /// Creates a content hash from raw SHA-256 digest bytes.
    #[must_use]
    pub const fn from_bytes(bytes: [u8; DIGEST_LEN]) -> Self {
        Self(bytes)
    }

    /// Returns the raw SHA-256 digest bytes.
    #[must_use]
    pub const fn as_bytes(&self) -> &[u8; DIGEST_LEN] {
        &self.0
    }
}

/// Errors produced when parsing a [`ContentHash`] textual form.
#[derive(thiserror::Error, Clone, Debug, PartialEq, Eq)]
pub enum ContentHashParseError {
    /// The text was not exactly 64 ASCII hexadecimal characters.
    #[error("content hash text must be 64 lowercase hexadecimal characters, found {found} bytes")]
    InvalidLength {
        /// Number of bytes found in the supplied text.
        found: usize,
    },

    /// The text contained a character outside lowercase hexadecimal.
    #[error("content hash text contains non-lowercase-hex byte 0x{byte:02x} at byte index {index}")]
    InvalidCharacter {
        /// Byte index of the invalid character.
        index: usize,
        /// Invalid byte found at `index`.
        byte: u8,
    },
}

/// Computes the package version hash over the canonical BEAM set only.
///
/// The SHA-256 algorithm is mandated by the `.aion` format contract so packers
/// and loaders on different hosts agree. Each module contributes its logical
/// name and exact bytes in [`BeamSet`] canonical order, with each field framed by
/// an eight-byte big-endian length prefix. This unambiguous framing prevents a
/// shifted name/body boundary from producing the same digest.
#[must_use]
pub fn content_hash(beams: &BeamSet) -> ContentHash {
    let mut digest = Sha256::new();
    update_beams(&mut digest, beams);
    ContentHash(digest.finalize().into())
}

/// Computes an explicit-timeout package version from the canonical BEAM set,
/// then the framed ASCII domain `aion.package.version.workflow-timeout.v1`,
/// then exactly 12 timeout bytes: seconds as `u64` big-endian followed by
/// subsecond nanoseconds as `u32` big-endian.
///
/// This single-entry form is retained for external callers; the per-entry
/// [`content_hash_with_timeouts`] is the authority the loader trusts, because it
/// binds every workflow entry's timeout — not only the primary — into identity.
#[must_use]
pub fn content_hash_with_timeout(beams: &BeamSet, timeout: Duration) -> ContentHash {
    let mut digest = Sha256::new();
    update_beams(&mut digest, beams);
    update_framed(&mut digest, WORKFLOW_TIMEOUT_DOMAIN);
    digest.update(timeout.as_secs().to_be_bytes());
    digest.update(timeout.subsec_nanos().to_be_bytes());
    ContentHash(digest.finalize().into())
}

/// Computes the per-entry timeout-bearing package version over the canonical
/// BEAM set, then the framed ASCII domain
/// `aion.package.version.workflow-timeouts.v3`, then a UNIFORM canonical encoding
/// that treats the primary entry and every additional entry alike: the total
/// entry count as `u64` big-endian, then — for the primary first and each
/// additional entry in manifest order — the entry's framed routing identity
/// followed by its authored timeout.
///
/// The framed routing identity is `manifest.entry_module` for the primary (the
/// module the loader selects at `load.rs`) and `workflow_type` for each
/// additional entry (its start/child-spawn routing name). Binding the primary's
/// routing identity is what closes the v2 gap: re-pointing `entry_module` to a
/// different module in the same beam closure re-routes entry selection, so it
/// MUST change identity or an authenticated timeout could be reassigned to
/// another workflow entry under an unchanged version.
///
/// Each authored timeout is encoded presence-first (a single `1`/`0` byte),
/// followed — only when present — by seconds as `u64` big-endian and subsecond
/// nanoseconds as `u32` big-endian. Binding presence AND value AND the entry's
/// own routing identity, for every entry uniformly, means no entry's timeout or
/// routing can be swapped, added, or removed without changing the version hash:
/// declaredness is an authenticated per-entry property, never a package-wide
/// inference from the primary alone.
///
/// This supersedes the pre-release `.v2` layout (which bound only the primary's
/// timeout, not its routing identity); a `.v2`-stamped archive therefore decodes
/// as wholly undeclared, exactly like any non-matching identity.
#[must_use]
pub fn content_hash_with_timeouts(beams: &BeamSet, manifest: &Manifest) -> ContentHash {
    let mut digest = Sha256::new();
    update_beams(&mut digest, beams);
    update_framed(&mut digest, WORKFLOW_TIMEOUTS_DOMAIN);
    update_timeouts(&mut digest, manifest);
    ContentHash(digest.finalize().into())
}

/// Computes the single `.v4` package identity over canonical BEAMs, the full
/// `.v3` routing/timeout vector, and the canonical durable contract record.
///
/// This is one domain-separated digest, not a tuple of independently checkable
/// hashes. A change to code, routing, timeouts, or any contract field therefore
/// changes the package identity at the same boundary.
#[must_use]
pub fn content_hash_with_contract(
    beams: &BeamSet,
    manifest: &Manifest,
    contract: &PackageContract,
) -> ContentHash {
    let mut digest = Sha256::new();
    update_beams(&mut digest, beams);
    update_framed(&mut digest, WORKER_CONTRACT_DOMAIN);
    update_timeouts(&mut digest, manifest);
    update_framed(&mut digest, &contract.canonical_bytes());
    ContentHash(digest.finalize().into())
}

fn update_timeouts(digest: &mut Sha256, manifest: &Manifest) {
    let entry_count = 1 + manifest.additional_workflows.len() as u64;
    digest.update(entry_count.to_be_bytes());
    update_framed(digest, manifest.entry_module.as_bytes());
    update_timeout_field(digest, manifest.timeout);
    for entry in &manifest.additional_workflows {
        update_framed(digest, entry.workflow_type.as_bytes());
        update_timeout_field(digest, entry.timeout);
    }
}

/// Whether this package's version identity commits to explicitly authored
/// per-entry workflow timeouts.
///
/// True only when the stored content hash is the domain-separated per-entry
/// timeout-bearing `.v3` identity ([`content_hash_with_timeouts`]) — never the
/// beams-only legacy identity, and never a superseded pre-release `.v1`/`.v2`
/// identity. A legacy (beams-only) archive, a pre-release single-value archive,
/// or one whose routing/additional entries were not uniformly bound therefore
/// reads as wholly NOT declared: no entry can arm a deadline. The check is
/// tamper-evident: the timeout value returned by [`crate::Package`] for any
/// entry is provably the one baked into the version hash, so a hand-edited or
/// injected per-entry timeout that was not part of the identity cannot fake
/// declaredness.
#[cfg(test)]
pub(crate) fn has_explicit_timeout_identity(
    beams: &BeamSet,
    manifest: &Manifest,
    hash: &ContentHash,
) -> bool {
    hash != &content_hash(beams) && hash == &content_hash_with_timeouts(beams, manifest)
}

/// Whether the package identity commits to its complete `.v4` contract record.
pub(crate) fn has_contract_identity(
    beams: &BeamSet,
    manifest: &Manifest,
    contract: Option<&PackageContract>,
    hash: &ContentHash,
) -> bool {
    contract.is_some_and(|contract| hash == &content_hash_with_contract(beams, manifest, contract))
}

/// Verifies an archive that may carry a `.v4` contract record.
pub(crate) fn verified_content_hash_with_contract(
    beams: &BeamSet,
    manifest: &Manifest,
    contract: Option<&PackageContract>,
) -> Result<ContentHash, PackageError> {
    if let Some(contract) = contract {
        let contract_hash = content_hash_with_contract(beams, manifest, contract);
        if manifest.version.as_str() == contract_hash.to_string() {
            return Ok(contract_hash);
        }
        // A contract-bearing archive whose stored identity matches neither
        // the current `.v5` recompute nor any legacy form is refused with
        // the CONTRACT-BEARING hash in the report: an archive minted under
        // the superseded `.v4` domain lands here, and the cure — redeploy
        // under the current identity — is the same as for tampering. This
        // build carries no `.v4` encoder by policy, so the two causes are
        // indistinguishable and both refuse.
        return verified_content_hash(beams, manifest).map_err(|error| match error {
            PackageError::IntegrityMismatch { expected, .. } => PackageError::IntegrityMismatch {
                expected,
                computed: contract_hash.to_string(),
            },
            other => other,
        });
    }
    verified_content_hash(beams, manifest)
}

/// Verifies the stored manifest version against the recomputed identities and
/// returns the matching hash, or an integrity error.
///
/// Three forms load. The beams-only legacy identity and the per-entry `.v3`
/// timeout-bearing identity both hold for freshly written archives; only the
/// `.v3` form makes [`has_explicit_timeout_identity`] true (declaring).
///
/// The third is a migration accommodation: a pre-release `.v1` single-value
/// identity ([`content_hash_with_timeout`], stamped only when a primary timeout
/// was present) is accepted as INTEGRITY-VALID BUT WHOLLY UNDECLARING. Its beam
/// closure is still authenticated by the `.v1` hash, so loading it is honest;
/// but it did not bind routing identity or additional entries under the current
/// law, so it is untrustworthy as a per-entry declaration and every entry reads
/// undeclared (nothing arms). This lets a `.v1`-stamped deployment recover on
/// restart instead of being skipped, without ever arming a deadline whose
/// authorship the current identity cannot vouch for. A `.v2` archive (never
/// released, and which likewise did not bind routing identity) is deliberately
/// NOT accommodated: it matches none of these forms and is rejected.
pub(crate) fn verified_content_hash(
    beams: &BeamSet,
    manifest: &Manifest,
) -> Result<ContentHash, PackageError> {
    let legacy_hash = content_hash(beams);
    let stored = manifest.version.as_str();
    if stored == legacy_hash.to_string() {
        return Ok(legacy_hash);
    }
    let timeouts_hash = content_hash_with_timeouts(beams, manifest);
    if stored == timeouts_hash.to_string() {
        return Ok(timeouts_hash);
    }
    // Migration: a pre-release `.v1` single-primary-timeout archive is accepted
    // as integrity-valid but non-declaring. `has_explicit_timeout_identity`
    // returns false for it (it is not the `.v3` hash), so it loads yet arms
    // nothing.
    if let Some(primary) = manifest.timeout {
        let v1_hash = content_hash_with_timeout(beams, primary);
        if stored == v1_hash.to_string() {
            return Ok(v1_hash);
        }
    }
    Err(PackageError::IntegrityMismatch {
        expected: stored.to_owned(),
        computed: legacy_hash.to_string(),
    })
}

/// Frames one entry's optional authored timeout into the digest: a presence
/// byte, then seconds (`u64` big-endian) and subsecond nanoseconds (`u32`
/// big-endian) only when a timeout is present. An absent timeout contributes
/// exactly the `0` presence byte, so presence and value are both bound.
fn update_timeout_field(digest: &mut Sha256, timeout: Option<Duration>) {
    match timeout {
        Some(timeout) => {
            digest.update([1_u8]);
            digest.update(timeout.as_secs().to_be_bytes());
            digest.update(timeout.subsec_nanos().to_be_bytes());
        }
        None => digest.update([0_u8]),
    }
}

fn update_beams(digest: &mut Sha256, beams: &BeamSet) {
    for module in beams.iter() {
        update_framed(digest, module.name().as_bytes());
        update_framed(digest, module.bytes());
    }
}

fn update_framed(digest: &mut Sha256, bytes: &[u8]) {
    let length = bytes.len() as u64;
    digest.update(length.to_be_bytes().as_slice());
    digest.update(bytes);
}

impl fmt::Display for ContentHash {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        for byte in &self.0 {
            write!(formatter, "{byte:02x}")?;
        }

        Ok(())
    }
}

impl FromStr for ContentHash {
    type Err = ContentHashParseError;

    fn from_str(text: &str) -> Result<Self, Self::Err> {
        let bytes = text.as_bytes();
        if bytes.len() != TEXT_LEN {
            return Err(ContentHashParseError::InvalidLength { found: bytes.len() });
        }

        let mut digest = [0_u8; DIGEST_LEN];
        for (index, pair) in bytes.chunks_exact(2).enumerate() {
            let high_index = index * 2;
            let low_index = high_index + 1;
            digest[index] = (hex_value(pair[0], high_index)? << 4) | hex_value(pair[1], low_index)?;
        }

        Ok(Self(digest))
    }
}

fn hex_value(byte: u8, index: usize) -> Result<u8, ContentHashParseError> {
    match byte {
        b'0'..=b'9' => Ok(byte - b'0'),
        b'a'..=b'f' => Ok(byte - b'a' + 10),
        _ => Err(ContentHashParseError::InvalidCharacter { index, byte }),
    }
}

impl Serialize for ContentHash {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_str(&self.to_string())
    }
}

impl<'de> Deserialize<'de> for ContentHash {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        deserializer.deserialize_str(ContentHashVisitor)
    }
}

struct ContentHashVisitor;

impl de::Visitor<'_> for ContentHashVisitor {
    type Value = ContentHash;

    fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.write_str("a 64-character lowercase hexadecimal SHA-256 content hash")
    }

    fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
    where
        E: de::Error,
    {
        ContentHash::from_str(value).map_err(E::custom)
    }
}

#[cfg(test)]
mod tests {
    use std::time::Duration;

    use serde_json::json;

    use super::{
        ContentHash, content_hash, content_hash_with_timeout, content_hash_with_timeouts,
        has_explicit_timeout_identity, verified_content_hash,
    };
    use crate::{
        BeamModule, BeamSet, CURRENT_FORMAT_VERSION, Manifest, ManifestVersion, PackageError,
        WorkflowEntry,
    };

    fn manifest_with(primary: Option<Duration>, additional: Vec<WorkflowEntry>) -> Manifest {
        Manifest {
            entry_module: "workflow/a".to_owned(),
            entry_function: "run".to_owned(),
            input_schema: json!({ "type": "object" }),
            output_schema: json!({ "type": "object" }),
            timeout: primary,
            activities: Vec::new(),
            version: ManifestVersion::new("unstamped"),
            format_version: CURRENT_FORMAT_VERSION,
            additional_workflows: additional,
        }
    }

    fn additional_entry(workflow_type: &str, timeout: Option<Duration>) -> WorkflowEntry {
        WorkflowEntry {
            workflow_type: workflow_type.to_owned(),
            entry_module: "workflow/a".to_owned(),
            entry_function: format!("{workflow_type}_run"),
            input_schema: json!({ "type": "object" }),
            output_schema: json!({ "type": "object" }),
            timeout,
            internal: true,
        }
    }

    #[test]
    fn content_hash_is_independent_of_insertion_order() -> Result<(), PackageError> {
        let first = BeamSet::new(vec![
            BeamModule::new("workflow/c", vec![3]),
            BeamModule::new("workflow/a", vec![1]),
            BeamModule::new("workflow/b", vec![2]),
        ])?;
        let second = BeamSet::new(vec![
            BeamModule::new("workflow/b", vec![2]),
            BeamModule::new("workflow/c", vec![3]),
            BeamModule::new("workflow/a", vec![1]),
        ])?;

        assert_eq!(content_hash(&first), content_hash(&second));

        Ok(())
    }

    #[test]
    fn legacy_identity_remains_exactly_the_beams_only_hash() -> Result<(), PackageError> {
        let beams = BeamSet::new(vec![BeamModule::new("workflow/a", vec![1, 2, 3])])?;
        let pre_change_rule = content_hash(&beams);
        assert_eq!(content_hash(&beams), pre_change_rule);
        Ok(())
    }

    #[test]
    fn explicit_timeout_identity_is_deterministic_and_value_sensitive() -> Result<(), PackageError>
    {
        let beams = BeamSet::new(vec![BeamModule::new("workflow/a", vec![1, 2, 3])])?;
        let two_hours = content_hash_with_timeout(&beams, Duration::from_secs(7_200));
        assert_eq!(
            two_hours,
            content_hash_with_timeout(&beams, Duration::from_secs(7_200))
        );
        assert_ne!(
            two_hours,
            content_hash_with_timeout(&beams, Duration::from_secs(21_600))
        );
        assert_ne!(
            two_hours,
            content_hash_with_timeout(&beams, Duration::new(7_200, 500_000_000))
        );
        assert_ne!(two_hours, content_hash(&beams));
        Ok(())
    }

    #[test]
    fn per_entry_identity_binds_every_additional_entry_timeout() -> Result<(), PackageError> {
        let beams = BeamSet::new(vec![BeamModule::new("workflow/a", vec![1, 2, 3])])?;
        let base = manifest_with(
            Some(Duration::from_secs(60)),
            vec![additional_entry("child", Some(Duration::from_secs(30)))],
        );

        // Changing an additional entry's timeout value changes the identity.
        let changed_value = manifest_with(
            Some(Duration::from_secs(60)),
            vec![additional_entry("child", Some(Duration::from_secs(31)))],
        );
        assert_ne!(
            content_hash_with_timeouts(&beams, &base),
            content_hash_with_timeouts(&beams, &changed_value),
        );

        // Adding an unbound additional timeout (the mixed-archive attack) changes
        // the identity: it cannot ride the primary's declaredness.
        let injected = manifest_with(
            Some(Duration::from_secs(60)),
            vec![additional_entry("child", Some(Duration::from_secs(3_600)))],
        );
        assert_ne!(
            content_hash_with_timeouts(&beams, &base),
            content_hash_with_timeouts(&beams, &injected),
        );

        // Presence alone (Some vs None) changes the identity.
        let absent = manifest_with(
            Some(Duration::from_secs(60)),
            vec![additional_entry("child", None)],
        );
        assert_ne!(
            content_hash_with_timeouts(&beams, &base),
            content_hash_with_timeouts(&beams, &absent),
        );
        Ok(())
    }

    #[test]
    fn v3_identity_binds_the_primary_routing_identity() -> Result<(), PackageError> {
        // Two modules in one closure. Re-pointing the primary `entry_module`
        // from one to the other re-routes entry selection, so it MUST change the
        // version identity — otherwise an authenticated primary timeout could be
        // reassigned to a different selected workflow (the v2 blocker).
        let beams = BeamSet::new(vec![
            BeamModule::new("workflow/a", vec![1, 2, 3]),
            BeamModule::new("workflow/b", vec![4, 5, 6]),
        ])?;
        let on_a = manifest_with(Some(Duration::from_secs(60)), Vec::new());
        let mut on_b = on_a.clone();
        on_b.entry_module = "workflow/b".to_owned();
        assert_ne!(
            content_hash_with_timeouts(&beams, &on_a),
            content_hash_with_timeouts(&beams, &on_b),
            "re-routing the primary entry_module changes identity",
        );
        // The stored `.v3` hash for A does not authenticate B's selection: with
        // B routed, A's stored identity reads as undeclared.
        let stored_for_a = content_hash_with_timeouts(&beams, &on_a);
        assert!(!has_explicit_timeout_identity(&beams, &on_b, &stored_for_a));
        assert!(has_explicit_timeout_identity(&beams, &on_a, &stored_for_a));
        Ok(())
    }

    #[test]
    fn v1_single_value_archive_loads_but_reads_undeclared() -> Result<(), PackageError> {
        // A pre-release `.v1` single-primary-timeout archive is accepted by
        // `verified_content_hash` (its beam closure is authenticated) but is
        // wholly undeclared: nothing arms. This keeps a `.v1`-stamped deployment
        // loadable on restart without arming a timeout the current identity law
        // cannot vouch for.
        let beams = BeamSet::new(vec![BeamModule::new("workflow/a", vec![1, 2, 3])])?;
        let mut manifest = manifest_with(Some(Duration::from_secs(60)), Vec::new());
        let v1 = content_hash_with_timeout(&beams, Duration::from_secs(60));
        manifest.version = ManifestVersion::new(v1.to_string());
        assert_eq!(verified_content_hash(&beams, &manifest)?, v1);
        assert!(!has_explicit_timeout_identity(&beams, &manifest, &v1));
        Ok(())
    }

    #[test]
    fn non_v1_non_v3_timeout_identity_is_rejected() -> Result<(), PackageError> {
        // Any non-legacy, non-`.v1`, non-`.v3` stored value (the pre-release
        // `.v2` shape among them) matches none of the accepted forms and is
        // rejected rather than silently loaded.
        let beams = BeamSet::new(vec![BeamModule::new("workflow/a", vec![1, 2, 3])])?;
        let mut manifest = manifest_with(Some(Duration::from_secs(60)), Vec::new());
        manifest.version = ManifestVersion::new("f".repeat(64));
        assert!(matches!(
            verified_content_hash(&beams, &manifest),
            Err(PackageError::IntegrityMismatch { .. })
        ));
        Ok(())
    }

    #[test]
    fn mixed_archive_with_injected_additional_timeout_reads_as_undeclared()
    -> Result<(), PackageError> {
        // A package whose stored hash bound ONLY the primary timeout (the old
        // single-entry identity) but which carries an additional entry with an
        // unauthenticated `Some(1h)` must read as wholly undeclared under the
        // per-entry identity: the stored hash matches neither the legacy nor the
        // per-entry timeout-bearing hash.
        let beams = BeamSet::new(vec![BeamModule::new("workflow/a", vec![1, 2, 3])])?;
        let manifest = manifest_with(
            Some(Duration::from_secs(60)),
            vec![additional_entry("child", Some(Duration::from_secs(3_600)))],
        );
        // The attacker stamps the primary-only identity as the version.
        let primary_only = content_hash_with_timeout(&beams, Duration::from_secs(60));
        assert!(
            !has_explicit_timeout_identity(&beams, &manifest, &primary_only),
            "an injected additional timeout cannot ride the primary-only identity"
        );
        // The beams-only legacy identity is likewise undeclared.
        assert!(!has_explicit_timeout_identity(
            &beams,
            &manifest,
            &content_hash(&beams)
        ));
        // Only the full per-entry identity authenticates every entry.
        assert!(has_explicit_timeout_identity(
            &beams,
            &manifest,
            &content_hash_with_timeouts(&beams, &manifest)
        ));
        Ok(())
    }

    #[test]
    fn content_hash_changes_when_a_module_byte_changes() -> Result<(), PackageError> {
        let original = BeamSet::new(vec![
            BeamModule::new("workflow/a", vec![1, 2, 3]),
            BeamModule::new("workflow/b", vec![4, 5, 6]),
        ])?;
        let changed = BeamSet::new(vec![
            BeamModule::new("workflow/a", vec![1, 2, 3]),
            BeamModule::new("workflow/b", vec![4, 5, 7]),
        ])?;

        assert_ne!(content_hash(&original), content_hash(&changed));

        Ok(())
    }

    #[test]
    fn content_hash_changes_when_a_module_name_changes() -> Result<(), PackageError> {
        let original = BeamSet::new(vec![BeamModule::new("workflow/a", vec![1, 2, 3])])?;
        let renamed = BeamSet::new(vec![BeamModule::new("workflow/renamed", vec![1, 2, 3])])?;

        assert_ne!(content_hash(&original), content_hash(&renamed));

        Ok(())
    }

    #[test]
    fn content_hash_framing_prevents_name_bytes_boundary_ambiguity() -> Result<(), PackageError> {
        let first = BeamSet::new(vec![BeamModule::new("ab", b"c".to_vec())])?;
        let second = BeamSet::new(vec![BeamModule::new("a", b"bc".to_vec())])?;

        assert_ne!(content_hash(&first), content_hash(&second));

        Ok(())
    }

    #[test]
    fn content_hash_text_round_trips() -> Result<(), PackageError> {
        let beams = BeamSet::new(vec![BeamModule::new("workflow/a", vec![0, 1, 2, 255])])?;
        let hash = content_hash(&beams);
        let text = hash.to_string();
        let parsed = text.parse::<ContentHash>();

        assert_eq!(text.len(), 64);
        assert!(
            text.bytes()
                .all(|byte| matches!(byte, b'0'..=b'9' | b'a'..=b'f'))
        );
        assert_eq!(parsed, Ok(hash));

        Ok(())
    }

    #[test]
    fn content_hash_rejects_uppercase_text() {
        let text = "A000000000000000000000000000000000000000000000000000000000000000";

        assert!(text.parse::<ContentHash>().is_err());
    }
}