harn_vm/value/
error.rs

1use harn_lexer::Span;
2
3use super::{VmDictExt, VmValue};
4
5/// Bound expressing how many arguments a callable accepts. Used in
6/// [`VmError::ArityMismatch`] so error messages can render the exact
7/// signature contract the caller violated.
8#[derive(Debug, Clone, Copy, PartialEq, Eq)]
9pub enum ArityExpect {
10    /// Exactly N parameters, no defaults, no rest.
11    Exact(usize),
12    /// `min..=max`: some params have defaults but the upper bound is fixed.
13    Range { min: usize, max: usize },
14    /// At least N parameters; further args land in a rest list. Used for
15    /// `print` / `log` / variadics.
16    AtLeast(usize),
17}
18
19impl std::fmt::Display for ArityExpect {
20    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
21        match self {
22            ArityExpect::Exact(n) => write!(f, "{n}"),
23            ArityExpect::Range { min, max } => write!(f, "{min}..={max}"),
24            ArityExpect::AtLeast(n) => write!(f, "at least {n}"),
25        }
26    }
27}
28
29#[derive(Debug, Clone)]
30pub struct ArityMismatchError {
31    pub callee: String,
32    pub expected: ArityExpect,
33    pub got: usize,
34    pub span: Option<Span>,
35}
36
37#[derive(Debug, Clone, Copy, PartialEq, Eq)]
38pub enum DeadlockDiagnostic {
39    SelfDeadlock,
40    WaitForGraph,
41}
42
43impl DeadlockDiagnostic {
44    fn code(self) -> &'static str {
45        match self {
46            Self::SelfDeadlock => "HARN-ORC-011",
47            Self::WaitForGraph => "HARN-ORC-012",
48        }
49    }
50}
51
52/// Payload for [`VmError::Deadlock`]. `kind` is the primitive kind
53/// (`"mutex"`, `"channel"`) or `"task"`; `key` is the primitive key or task
54/// id; `detail` names the specific footgun.
55#[derive(Debug, Clone)]
56pub struct DeadlockError {
57    pub diagnostic: DeadlockDiagnostic,
58    pub kind: String,
59    pub key: String,
60    pub detail: String,
61}
62
63impl DeadlockError {
64    pub(crate) fn self_deadlock(
65        kind: impl Into<String>,
66        key: impl Into<String>,
67        detail: impl Into<String>,
68    ) -> Self {
69        Self {
70            diagnostic: DeadlockDiagnostic::SelfDeadlock,
71            kind: kind.into(),
72            key: key.into(),
73            detail: detail.into(),
74        }
75    }
76
77    pub(crate) fn wait_for_graph(
78        kind: impl Into<String>,
79        key: impl Into<String>,
80        detail: impl Into<String>,
81    ) -> Self {
82        Self {
83            diagnostic: DeadlockDiagnostic::WaitForGraph,
84            kind: kind.into(),
85            key: key.into(),
86            detail: detail.into(),
87        }
88    }
89}
90
91#[derive(Debug, Clone)]
92pub struct ArgTypeMismatchError {
93    pub callee: String,
94    pub param: String,
95    pub expected: String,
96    pub got: &'static str,
97    pub span: Option<Span>,
98}
99
100#[derive(Debug, Clone)]
101pub enum VmError {
102    StackUnderflow,
103    StackOverflow,
104    UndefinedVariable(String),
105    UndefinedBuiltin(String),
106    ImmutableAssignment(String),
107    TypeError(String),
108    Runtime(String),
109    DivisionByZero,
110    /// A host-imposed deadline expired while executing the VM. Unlike a Harn
111    /// `deadline` block, this control-plane stop cannot be caught by user code.
112    ExecutionDeadlineExceeded,
113    /// A Harn program requested that its embedding process terminate with this
114    /// status code. Like a host deadline, this is control flow rather than a
115    /// catchable Harn error; the embedding boundary owns the final cleanup and
116    /// process exit.
117    ProcessExit(i32),
118    /// A host dropped a polled top-level execution future. Interpreter state is
119    /// intentionally not resumed after arbitrary async cancellation. Discard
120    /// this VM; see [`crate::Vm::execute_with_timeout`] for ambient-state
121    /// cleanup requirements.
122    AbandonedExecution,
123    Thrown(VmValue),
124    /// Thrown with error category for structured error handling.
125    CategorizedError {
126        message: String,
127        category: ErrorCategory,
128    },
129    DaemonQueueFull {
130        daemon_id: String,
131        capacity: usize,
132    },
133    /// A deterministic, provably-unresolvable self-deadlock caught before the
134    /// VM would block forever (Rust's borrow checker prevents data races but
135    /// not deadlocks; this is the Go-runtime "all goroutines asleep" analogue
136    /// for the cases we can prove). Boxed — like [`VmError::ArityMismatch`] —
137    /// so the rare three-`String` payload doesn't enlarge `VmError` on the
138    /// pervasive `Result<VmValue, VmError>` hot path. Carries `HARN-ORC-011`.
139    Deadlock(Box<DeadlockError>),
140    Return(VmValue),
141    InvalidInstruction(u8),
142    /// Wrong number of arguments at a call site. Distinct from
143    /// [`VmError::TypeError`] so the runtime can match-and-recover (and
144    /// so error UX renders `expected 2..=3 got 1` consistently).
145    ArityMismatch(Box<ArityMismatchError>),
146    /// Argument value did not satisfy the declared parameter type.
147    /// `expected` is a pretty-printed type expression; `got` is the value's
148    /// runtime type name (`VmValue::type_name`). Used for both
149    /// user-defined function parameters (with declared types) and
150    /// registry-known builtin parameters.
151    ArgTypeMismatch(Box<ArgTypeMismatchError>),
152}
153
154impl VmError {
155    /// Whether this error is VM control flow that user `catch` blocks and
156    /// error-as-data combinators must propagate unchanged.
157    pub fn is_uncatchable_control_flow(&self) -> bool {
158        matches!(self, Self::ExecutionDeadlineExceeded | Self::ProcessExit(_))
159    }
160
161    /// The requested host-process exit status, when this is an explicit Harn
162    /// `exit(code)` control signal.
163    pub fn process_exit_code(&self) -> Option<i32> {
164        match self {
165            Self::ProcessExit(code) => Some(*code),
166            _ => None,
167        }
168    }
169
170    /// The `VmValue` a `catch` binding (or a `parallel settle` result) observes
171    /// for this error: the raw thrown value for [`VmError::Thrown`] (so a
172    /// structured error — e.g. a `{category, message}` dict from `throw_error` —
173    /// keeps its shape and category), a structured `{category, message}` dict for
174    /// [`VmError::CategorizedError`] (so consumers branch on the typed category
175    /// rather than substring-matching rendered prose), otherwise the rendered
176    /// message.
177    ///
178    /// Single source of truth for VM-error-to-value lowering so every seam that
179    /// surfaces a caught error to Harn (`try`/`catch` via `handle_error`,
180    /// `parallel settle`) exposes identical, structure-preserving values. Before
181    /// this was shared, `parallel settle` stringified errors via `to_string()`,
182    /// so a categorized error thrown in a settle branch lost its category (a
183    /// `cancelled`/`internal` fault that must propagate looked `generic`).
184    ///
185    /// The `category` key uses [`ErrorCategory::as_str`] — a canonical,
186    /// exhaustively-matched snake_case contract — so a new variant added there
187    /// is compiler-forced to name its key. `message` preserves the original
188    /// rendered text, so a `catch` that stringifies the caught value still reads
189    /// sensibly (the dict renders both fields).
190    pub fn thrown_value(&self) -> VmValue {
191        match self {
192            VmError::Thrown(v) => v.clone(),
193            VmError::CategorizedError { message, category } => {
194                let mut dict = std::collections::BTreeMap::new();
195                dict.put_str("category", category.as_str());
196                dict.put_str("message", message);
197                VmValue::dict(dict)
198            }
199            other => VmValue::String(arcstr::ArcStr::from(other.to_string())),
200        }
201    }
202}
203
204/// Error categories for structured error handling in agent orchestration.
205#[derive(Debug, Clone, PartialEq, Eq)]
206pub enum ErrorCategory {
207    /// Network/connection timeout
208    Timeout,
209    /// Authentication/authorization failure
210    Auth,
211    /// Rate limit exceeded (HTTP 429 / quota)
212    RateLimit,
213    /// Upstream provider is overloaded (HTTP 503 / 529).
214    /// Distinct from RateLimit: the client hasn't exceeded a quota — the
215    /// provider is shedding load and will recover on its own.
216    Overloaded,
217    /// Provider-side 5xx error (500, 502) that isn't specifically overload.
218    ServerError,
219    /// Network-level transient failure (connection reset, DNS hiccup,
220    /// partial stream) — retryable but not provider-status-coded.
221    TransientNetwork,
222    /// A shared local resource is temporarily unavailable, such as a
223    /// contended database write lock.
224    ResourceBusy,
225    /// LLM output failed schema validation. Retryable via `schema_retries`.
226    SchemaValidation,
227    /// LLM streaming response was aborted mid-stream because the partial
228    /// JSON content could not conceivably satisfy `output_schema`. Surfaced
229    /// by `llm_call` when `schema_stream_abort` is on (the default for
230    /// schema-bearing calls). Consumes one `schema_retries` budget slot;
231    /// the retry replays the prompt with a corrective nudge that cites
232    /// the abort path + reason.
233    SchemaStreamAborted,
234    /// Tool execution failure
235    ToolError,
236    /// Tool was rejected by the host (not permitted / not in allowlist)
237    ToolRejected,
238    /// Outbound network egress was blocked by policy.
239    EgressBlocked,
240    /// Operation was cancelled
241    Cancelled,
242    /// Channel was closed before the operation could complete.
243    ChannelClosed,
244    /// Resource not found
245    NotFound,
246    /// Circuit breaker is open
247    CircuitOpen,
248    /// LLM cost or token budget would be exceeded
249    BudgetExceeded,
250    /// An internal engine/wiring bug — an undefined builtin, corrupt bytecode,
251    /// or another VM invariant violation that no amount of retrying or model
252    /// reasoning can fix. Distinct from `Generic` so callers (notably the agent
253    /// loop) can re-raise it loudly instead of folding it into a tool-error
254    /// observation and marching on to a `done` status. This is the category
255    /// that keeps a mis-wired builtin (e.g. a `#[harn_builtin]` def missing
256    /// from its install array) from shipping silently inert.
257    Internal,
258    /// A host environment / infrastructure problem that is not the workload's
259    /// code defect: a required developer-toolchain root or cache lies outside
260    /// the sandbox profile, a needed system binary is missing, or another
261    /// machine-provisioning gap. Distinct from `ToolRejected` (the host
262    /// deliberately refused an action) and `Internal` (an engine bug): the fix
263    /// is to widen the sandbox/config or provision the host, not to change the
264    /// agent's code. Callers (and embedders) branch on this to avoid blaming
265    /// the model for an environment gap.
266    Environment,
267    /// Generic/unclassified error
268    Generic,
269}
270
271impl ErrorCategory {
272    /// Every category, in declaration order.
273    ///
274    /// Sibling taxonomies (`ToolCallErrorCategory::ALL`,
275    /// `AgentTerminalKind::ALL`) already publish theirs, and code that has to
276    /// decide something for EVERY category — a wire projection, a docs table,
277    /// a round-trip guard — needs to enumerate them. While this list lived in
278    /// one module's test scope, the tool-call wire projection could not consult
279    /// it, and a category with no decided wire bucket went unnoticed (#5537).
280    pub const ALL: [Self; 20] = [
281        Self::Timeout,
282        Self::Auth,
283        Self::RateLimit,
284        Self::Overloaded,
285        Self::ServerError,
286        Self::TransientNetwork,
287        Self::ResourceBusy,
288        Self::SchemaValidation,
289        Self::SchemaStreamAborted,
290        Self::ToolError,
291        Self::ToolRejected,
292        Self::EgressBlocked,
293        Self::Cancelled,
294        Self::ChannelClosed,
295        Self::NotFound,
296        Self::CircuitOpen,
297        Self::BudgetExceeded,
298        Self::Internal,
299        Self::Environment,
300        Self::Generic,
301    ];
302
303    pub fn as_str(&self) -> &'static str {
304        match self {
305            ErrorCategory::Timeout => "timeout",
306            ErrorCategory::Auth => "auth",
307            ErrorCategory::RateLimit => "rate_limit",
308            ErrorCategory::Overloaded => "overloaded",
309            ErrorCategory::ServerError => "server_error",
310            ErrorCategory::TransientNetwork => "transient_network",
311            ErrorCategory::ResourceBusy => "resource_busy",
312            ErrorCategory::SchemaValidation => "schema_validation",
313            ErrorCategory::SchemaStreamAborted => "schema_stream_aborted",
314            ErrorCategory::ToolError => "tool_error",
315            ErrorCategory::ToolRejected => "tool_rejected",
316            ErrorCategory::EgressBlocked => "egress_blocked",
317            ErrorCategory::Cancelled => "cancelled",
318            ErrorCategory::ChannelClosed => "channel_closed",
319            ErrorCategory::NotFound => "not_found",
320            ErrorCategory::CircuitOpen => "circuit_open",
321            ErrorCategory::BudgetExceeded => "budget_exceeded",
322            ErrorCategory::Internal => "internal",
323            ErrorCategory::Environment => "environment",
324            ErrorCategory::Generic => "generic",
325        }
326    }
327
328    pub fn parse(s: &str) -> Self {
329        match s {
330            "timeout" => ErrorCategory::Timeout,
331            "auth" => ErrorCategory::Auth,
332            "rate_limit" => ErrorCategory::RateLimit,
333            "overloaded" => ErrorCategory::Overloaded,
334            "server_error" => ErrorCategory::ServerError,
335            "transient_network" => ErrorCategory::TransientNetwork,
336            "resource_busy" => ErrorCategory::ResourceBusy,
337            "schema_validation" => ErrorCategory::SchemaValidation,
338            "schema_stream_aborted" => ErrorCategory::SchemaStreamAborted,
339            "tool_error" => ErrorCategory::ToolError,
340            "tool_rejected" => ErrorCategory::ToolRejected,
341            "egress_blocked" => ErrorCategory::EgressBlocked,
342            "cancelled" => ErrorCategory::Cancelled,
343            "channel_closed" => ErrorCategory::ChannelClosed,
344            "not_found" => ErrorCategory::NotFound,
345            "circuit_open" => ErrorCategory::CircuitOpen,
346            "budget_exceeded" => ErrorCategory::BudgetExceeded,
347            "internal" => ErrorCategory::Internal,
348            "environment" => ErrorCategory::Environment,
349            _ => ErrorCategory::Generic,
350        }
351    }
352
353    /// Whether this category represents an internal engine/wiring bug that must
354    /// be surfaced rather than retried or swallowed as a recoverable failure.
355    pub fn is_internal(&self) -> bool {
356        matches!(self, ErrorCategory::Internal)
357    }
358
359    /// Whether an error of this category is worth retrying because the
360    /// underlying condition is transient. Agent loops consult this to decide
361    /// whether to back off and retry vs surface the error to the user.
362    pub fn is_transient(&self) -> bool {
363        matches!(
364            self,
365            ErrorCategory::Timeout
366                | ErrorCategory::RateLimit
367                | ErrorCategory::Overloaded
368                | ErrorCategory::ServerError
369                | ErrorCategory::TransientNetwork
370                | ErrorCategory::ResourceBusy
371        )
372    }
373}
374
375/// Create a categorized error conveniently.
376pub fn categorized_error(message: impl Into<String>, category: ErrorCategory) -> VmError {
377    VmError::CategorizedError {
378        message: message.into(),
379        category,
380    }
381}
382
383/// Extract error category from a VmError.
384///
385/// Classification priority:
386/// 1. Explicit CategorizedError variant (set by throw_error or internal code)
387/// 2. Thrown dict with a "category" field (user-created structured errors)
388/// 3. HTTP status code extraction (standard, unambiguous)
389/// 4. Deadline exceeded (VM-internal)
390/// 5. Fallback to Generic
391pub fn error_to_category(err: &VmError) -> ErrorCategory {
392    match err {
393        VmError::ExecutionDeadlineExceeded => ErrorCategory::Timeout,
394        // ProcessExit is uncatchable control flow rather than an agent-facing
395        // failure. Keep this fallback total for callers that classify an
396        // arbitrary VmError without treating the request as retryable.
397        VmError::ProcessExit(_) => ErrorCategory::Generic,
398        VmError::AbandonedExecution => ErrorCategory::Cancelled,
399        VmError::CategorizedError { category, .. } => category.clone(),
400        VmError::Thrown(VmValue::Dict(d)) => d
401            .get("category")
402            .map(|v| ErrorCategory::parse(&v.display()))
403            .unwrap_or(ErrorCategory::Generic),
404        VmError::Thrown(VmValue::String(s)) => classify_error_message(s),
405        VmError::Runtime(msg) => classify_error_message(msg),
406        // Engine/wiring bugs: an undefined builtin (declared but not installed,
407        // or a typo in stdlib/host code) or corrupt bytecode. No retry or model
408        // reasoning fixes these, so they get their own category the agent loop
409        // re-raises instead of swallowing.
410        VmError::UndefinedBuiltin(_) | VmError::InvalidInstruction(_) => ErrorCategory::Internal,
411        // A deadlock is permanently non-retryable and not provider-related —
412        // `Generic` is the correct "surface it, don't back off" bucket.
413        VmError::Deadlock(_) => ErrorCategory::Generic,
414        _ => ErrorCategory::Generic,
415    }
416}
417
418/// Classify an error message using HTTP status codes and well-known patterns.
419/// Prefers unambiguous signals (status codes) over substring heuristics.
420pub fn classify_error_message(msg: &str) -> ErrorCategory {
421    // 1. HTTP status codes — most reliable signal
422    if let Some(cat) = classify_by_http_status(msg) {
423        return cat;
424    }
425    // 2. Internal engine/wiring bug surfaced as a plain message. Some call
426    //    sites build `Runtime("Undefined builtin: …")` strings instead of the
427    //    structured `VmError::UndefinedBuiltin` variant; classify both the same
428    //    so the agent loop re-raises rather than swallows.
429    if msg.contains("Undefined builtin") {
430        return ErrorCategory::Internal;
431    }
432    // 3. Well-known error identifiers from major APIs
433    //    (Anthropic, OpenAI, and standard HTTP patterns)
434    let lower = msg.to_lowercase();
435    if lower.contains("cancelled") || lower.contains("canceled") {
436        return ErrorCategory::Cancelled;
437    }
438    if msg.contains("ChannelClosed") || lower.contains("channel closed") {
439        return ErrorCategory::ChannelClosed;
440    }
441    if msg.contains("Deadline exceeded") || msg.contains("context deadline exceeded") {
442        return ErrorCategory::Timeout;
443    }
444    if msg.contains("overloaded_error") {
445        // Anthropic overloaded_error surfaces as HTTP 529.
446        return ErrorCategory::Overloaded;
447    }
448    if msg.contains("api_error") {
449        // Anthropic catch-all server-side error.
450        return ErrorCategory::ServerError;
451    }
452    if msg.contains("insufficient_quota") || msg.contains("billing_hard_limit_reached") {
453        // OpenAI-specific quota error types.
454        return ErrorCategory::RateLimit;
455    }
456    if msg.contains("invalid_api_key") || msg.contains("authentication_error") {
457        return ErrorCategory::Auth;
458    }
459    if msg.contains("not_found_error") || msg.contains("model_not_found") {
460        return ErrorCategory::NotFound;
461    }
462    // OpenRouter reports an unknown model as HTTP 400 with the body
463    // "<id> is not a valid model ID" — no status-code or typed-error signal
464    // that `classify_by_http_status` / the checks above can latch onto. Map
465    // the prose to NotFound so it lines up with Cerebras's 404 path (and with
466    // `errors::is_model_unavailable`'s reason taxonomy).
467    if lower.contains("is not a valid model id") || lower.contains("invalid model id") {
468        return ErrorCategory::NotFound;
469    }
470    if msg.contains("circuit_open") {
471        return ErrorCategory::CircuitOpen;
472    }
473    // Network-level transient patterns (pre-HTTP-status, pre-provider-framing).
474    if lower.contains("connection reset")
475        || lower.contains("connection refused")
476        || lower.contains("connection closed")
477        || lower.contains("broken pipe")
478        || lower.contains("dns error")
479        || lower.contains("stream error")
480        || lower.contains("unexpected eof")
481    {
482        return ErrorCategory::TransientNetwork;
483    }
484    ErrorCategory::Generic
485}
486
487/// Classify errors by HTTP status code if one appears in the message.
488/// This is the most reliable classification method since status codes
489/// are standardized (RFC 9110) and unambiguous.
490fn classify_by_http_status(msg: &str) -> Option<ErrorCategory> {
491    // Extract 3-digit HTTP status codes from common patterns:
492    // "HTTP 429", "status 429", "429 Too Many", "error: 401"
493    for code in extract_http_status_codes(msg) {
494        return Some(match code {
495            401 | 403 => ErrorCategory::Auth,
496            404 | 410 => ErrorCategory::NotFound,
497            408 | 504 | 522 | 524 => ErrorCategory::Timeout,
498            429 => ErrorCategory::RateLimit,
499            503 | 529 => ErrorCategory::Overloaded,
500            500 | 502 => ErrorCategory::ServerError,
501            _ => continue,
502        });
503    }
504    None
505}
506
507/// Extract plausible HTTP status codes from an error message.
508fn extract_http_status_codes(msg: &str) -> Vec<u16> {
509    let mut codes = Vec::new();
510    let bytes = msg.as_bytes();
511    for i in 0..bytes.len().saturating_sub(2) {
512        // Look for 3-digit sequences in the 100-599 range
513        if bytes[i].is_ascii_digit()
514            && bytes[i + 1].is_ascii_digit()
515            && bytes[i + 2].is_ascii_digit()
516        {
517            // Ensure it's not part of a longer number
518            let before_ok = i == 0 || !bytes[i - 1].is_ascii_digit();
519            let after_ok = i + 3 >= bytes.len() || !bytes[i + 3].is_ascii_digit();
520            if before_ok && after_ok {
521                if let Ok(code) = msg[i..i + 3].parse::<u16>() {
522                    if (400..=599).contains(&code) {
523                        codes.push(code);
524                    }
525                }
526            }
527        }
528    }
529    codes
530}
531
532impl std::fmt::Display for VmError {
533    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
534        match self {
535            VmError::StackUnderflow => write!(f, "Stack underflow"),
536            VmError::StackOverflow => write!(f, "Stack overflow: too many nested calls"),
537            VmError::UndefinedVariable(n) => write!(f, "Undefined variable: {n}"),
538            VmError::UndefinedBuiltin(n) => write!(f, "Undefined builtin: {n}"),
539            VmError::ImmutableAssignment(n) => {
540                write!(f, "Cannot assign to immutable binding: {n}")
541            }
542            VmError::TypeError(msg) => write!(f, "Type error: {msg}"),
543            VmError::Runtime(msg) => write!(f, "Runtime error: {msg}"),
544            VmError::DivisionByZero => write!(f, "Division by zero"),
545            VmError::ExecutionDeadlineExceeded => write!(f, "Execution deadline exceeded"),
546            VmError::ProcessExit(code) => write!(f, "Process exit requested: {code}"),
547            VmError::AbandonedExecution => write!(
548                f,
549                "Execution future was abandoned; discard this VM and reset its exclusively owned execution context"
550            ),
551            VmError::Thrown(v) => write!(f, "Thrown: {}", v.display()),
552            VmError::CategorizedError { message, category } => {
553                write!(f, "Error [{}]: {}", category.as_str(), message)
554            }
555            VmError::DaemonQueueFull {
556                daemon_id,
557                capacity,
558            } => write!(
559                f,
560                "Daemon queue full: daemon '{daemon_id}' reached its event_queue_capacity of {capacity}"
561            ),
562            VmError::Deadlock(err) => match err.diagnostic {
563                DeadlockDiagnostic::SelfDeadlock => write!(
564                    f,
565                    "{}: deadlock detected: {} ({} '{}') — this wait can never complete and would block forever",
566                    err.diagnostic.code(),
567                    err.detail,
568                    err.kind,
569                    err.key
570                ),
571                DeadlockDiagnostic::WaitForGraph => write!(
572                    f,
573                    "{}: wait-for deadlock detected: {} ({} '{}') — no active task can make progress",
574                    err.diagnostic.code(),
575                    err.detail,
576                    err.kind,
577                    err.key
578                ),
579            },
580            VmError::Return(_) => write!(f, "Return from function"),
581            VmError::InvalidInstruction(op) => write!(f, "Invalid instruction: 0x{op:02x}"),
582            VmError::ArityMismatch(err) => {
583                let arg_word = match err.expected {
584                    ArityExpect::Exact(1) | ArityExpect::AtLeast(1) => "argument",
585                    _ => "arguments",
586                };
587                write!(
588                    f,
589                    "Arity mismatch: '{}' expects {} {}, got {}{}",
590                    err.callee,
591                    err.expected,
592                    arg_word,
593                    err.got,
594                    fmt_span_suffix(&err.span)
595                )
596            }
597            VmError::ArgTypeMismatch(err) => {
598                write!(
599                    f,
600                    "Type error: '{}' parameter `{}` expects {}, got {}{}",
601                    err.callee,
602                    err.param,
603                    err.expected,
604                    err.got,
605                    fmt_span_suffix(&err.span)
606                )
607            }
608        }
609    }
610}
611
612fn fmt_span_suffix(span: &Option<Span>) -> String {
613    match span {
614        Some(s) => format!(" (at byte {}..{})", s.start, s.end),
615        None => String::new(),
616    }
617}
618
619impl std::error::Error for VmError {}
620
621#[cfg(test)]
622mod tests {
623    use super::*;
624
625    /// A new variant must be added to [`ErrorCategory::ALL`], or the guards below
626    /// silently stop covering it. This match is the tripwire: it fails to
627    /// compile until the variant is named, and the arm points at the list.
628    #[test]
629    fn all_categories_is_exhaustive() {
630        for category in &ErrorCategory::ALL {
631            match category {
632                ErrorCategory::Timeout
633                | ErrorCategory::Auth
634                | ErrorCategory::RateLimit
635                | ErrorCategory::Overloaded
636                | ErrorCategory::ServerError
637                | ErrorCategory::TransientNetwork
638                | ErrorCategory::ResourceBusy
639                | ErrorCategory::SchemaValidation
640                | ErrorCategory::SchemaStreamAborted
641                | ErrorCategory::ToolError
642                | ErrorCategory::ToolRejected
643                | ErrorCategory::EgressBlocked
644                | ErrorCategory::Cancelled
645                | ErrorCategory::ChannelClosed
646                | ErrorCategory::NotFound
647                | ErrorCategory::CircuitOpen
648                | ErrorCategory::BudgetExceeded
649                | ErrorCategory::Internal
650                | ErrorCategory::Environment
651                | ErrorCategory::Generic => {}
652            }
653        }
654        assert_eq!(
655            ErrorCategory::ALL.len(),
656            20,
657            "a category was added or removed — update `ErrorCategory::ALL` and the \
658             `Error categories` table in docs/src/builtins.md"
659        );
660    }
661
662    #[test]
663    fn every_category_round_trips_through_parse() {
664        for category in &ErrorCategory::ALL {
665            assert_eq!(
666                &ErrorCategory::parse(category.as_str()),
667                category,
668                "`{}` does not round-trip — `parse` is missing an arm, so a \
669                 host handing this category back to Harn silently gets \
670                 `generic`",
671                category.as_str()
672            );
673        }
674    }
675
676    /// Scripts branch on these strings, so an undocumented category is a
677    /// caller writing a match that cannot handle a value the runtime emits.
678    /// `error_category()` used to advertise 10 of the full category set — a dead-port probe
679    /// returning `transient_network` fell outside its own documented list.
680    #[test]
681    fn every_category_is_documented_in_builtins_md() {
682        let path = concat!(env!("CARGO_MANIFEST_DIR"), "/../../docs/src/builtins.md");
683        let doc =
684            std::fs::read_to_string(path).unwrap_or_else(|err| panic!("cannot read {path}: {err}"));
685        let table = doc
686            .split_once("### Error categories")
687            .unwrap_or_else(|| {
688                panic!("docs/src/builtins.md lost its `### Error categories` section")
689            })
690            .1;
691        let table = table.split_once("\n## ").map_or(table, |(head, _)| head);
692        for category in &ErrorCategory::ALL {
693            let row = format!("| `{}` |", category.as_str());
694            assert!(
695                table.contains(&row),
696                "`{}` is missing from the `Error categories` table in \
697                 docs/src/builtins.md",
698                category.as_str()
699            );
700        }
701    }
702
703    #[test]
704    fn classifies_cancelled_messages() {
705        assert_eq!(
706            classify_error_message("Bridge: operation cancelled"),
707            ErrorCategory::Cancelled
708        );
709        assert_eq!(
710            classify_error_message("operation canceled by host"),
711            ErrorCategory::Cancelled
712        );
713    }
714
715    #[test]
716    fn classifies_undefined_builtin_as_internal() {
717        // Structured variant (dispatch table miss / uninstalled builtin).
718        assert_eq!(
719            error_to_category(&VmError::UndefinedBuiltin("__host_agent_foo".into())),
720            ErrorCategory::Internal
721        );
722        // Corrupt bytecode / compiler-VM opcode drift.
723        assert_eq!(
724            error_to_category(&VmError::InvalidInstruction(200)),
725            ErrorCategory::Internal
726        );
727        // Stringly form: some call sites build a `Runtime("Undefined builtin: …")`
728        // message instead of the structured variant — both must classify the same.
729        assert_eq!(
730            error_to_category(&VmError::Runtime(
731                "Undefined builtin: __host_agent_foo (did you mean `bar`?)".into()
732            )),
733            ErrorCategory::Internal
734        );
735        assert_eq!(
736            classify_error_message("Undefined builtin: __host_agent_foo"),
737            ErrorCategory::Internal
738        );
739        // Internal errors are never treated as transient/retryable.
740        assert!(!ErrorCategory::Internal.is_transient());
741        assert!(ErrorCategory::Internal.is_internal());
742        // Round-trips through the string form the agent loop compares against.
743        assert_eq!(ErrorCategory::Internal.as_str(), "internal");
744        assert_eq!(ErrorCategory::parse("internal"), ErrorCategory::Internal);
745    }
746
747    #[test]
748    fn classifies_openrouter_invalid_model_id_as_not_found() {
749        // OpenRouter reports an unknown model as HTTP 400 + prose. The 400 is
750        // not classified by status, so the prose substring must lift it to
751        // NotFound to match Cerebras's 404 path.
752        assert_eq!(
753            classify_error_message(
754                "openrouter API error: qwen/qwen3-coder-bogus is not a valid model ID"
755            ),
756            ErrorCategory::NotFound
757        );
758        assert_eq!(
759            classify_error_message("invalid model id supplied"),
760            ErrorCategory::NotFound
761        );
762    }
763
764    #[test]
765    fn categorized_error_lowers_to_structured_dict() {
766        // A caught `CategorizedError` must surface as a `{category, message}`
767        // dict so `.harn` consumers branch on the typed category instead of
768        // substring-matching the rendered prose (issue #4420).
769        let err = categorized_error(
770            "sandbox violation: /etc/passwd",
771            ErrorCategory::ToolRejected,
772        );
773        let VmValue::Dict(dict) = err.thrown_value() else {
774            panic!(
775                "categorized error must lower to a dict, got {:?}",
776                err.thrown_value()
777            );
778        };
779        assert_eq!(
780            dict.get("category").map(|v| v.display()).as_deref(),
781            Some("tool_rejected"),
782        );
783        assert_eq!(
784            dict.get("message").map(|v| v.display()).as_deref(),
785            Some("sandbox violation: /etc/passwd"),
786        );
787        // The key is the canonical, exhaustively-matched `ErrorCategory::as_str`
788        // contract — not the Display prose. A stringified catch still renders the
789        // message + category (so generic catch-and-log stays sensible).
790        let rendered = categorized_error("boom", ErrorCategory::Cancelled)
791            .thrown_value()
792            .display();
793        assert!(rendered.contains("cancelled"), "rendered dict: {rendered}");
794        assert!(rendered.contains("boom"), "rendered dict: {rendered}");
795    }
796
797    #[test]
798    fn thrown_value_passes_structured_thrown_through_unchanged() {
799        // A user `throw` of a structured value keeps its exact shape — the
800        // lowering seam must not stringify or re-wrap it.
801        let original = VmValue::dict(std::collections::BTreeMap::from([(
802            "code".to_string(),
803            VmValue::Int(7),
804        )]));
805        let VmValue::Dict(dict) = VmError::Thrown(original).thrown_value() else {
806            panic!("thrown dict must pass through as a dict");
807        };
808        assert!(matches!(dict.get("code"), Some(VmValue::Int(7))));
809    }
810
811    #[test]
812    fn deadlock_renders_with_stable_code() {
813        let err = VmError::Deadlock(Box::new(DeadlockError::self_deadlock(
814            "mutex",
815            "__default__",
816            "re-entrant acquire",
817        )));
818        assert!(
819            err.to_string().starts_with("HARN-ORC-011"),
820            "deadlock Display must carry the stable code: {err}"
821        );
822    }
823
824    #[test]
825    fn deadlock_maps_to_generic_category() {
826        let err = VmError::Deadlock(Box::new(DeadlockError::self_deadlock(
827            "task",
828            "task_1",
829            "self-join",
830        )));
831        let category = error_to_category(&err);
832        assert_eq!(category, ErrorCategory::Generic);
833        assert!(
834            !category.is_transient(),
835            "a deadlock must not be treated as a retryable transient error"
836        );
837    }
838}
harn_vm/value/error.rs

harn_vm/value/
error.rs
