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openspec/archive/2026-04-27-error-spec-tightening/specs/error/spec.md

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+## MODIFIED Requirements
+
+### Requirement: Zero workspace and runtime dependencies
+
+The `@suaveplan/error` package's `dependencies` MUST be limited to `tslib`, `zod`, and `@suaveplan/types`. No `peerDependencies`. No other `@suaveplan/*` packages at runtime. The `@suaveplan/types` carve-out is permitted exclusively because it ships zero runtime code (types-only build, byte-size guarded by its own conformance test) and therefore cannot reintroduce the circular foundation-of-foundations hazard the rule otherwise prevents.
+
+**Verified by:** `tests/no-disallowed.test.ts` and the `package.json` dep-set under `bunx turbo ls --filter=@suaveplan/error...`.
+
+#### Scenario: Dep-graph guard
+
+- **WHEN** `bunx turbo ls --filter=@suaveplan/error...` is run
+- **THEN** the only `@suaveplan/*` packages in the forward closure are `@suaveplan/error` itself and `@suaveplan/types`
+
+#### Scenario: No Node / browser built-ins
+
+- **WHEN** the built `dist/` is grep'd
+- **THEN** it MUST NOT reference `node:fs`, `node:path`, `node:url`, `process`, `Buffer`, `document`, `window`, or any DOM / Node-only API
+
+### Requirement: Cause-chain traversal is cycle-safe and depth-bounded
+
+The package SHALL export `walkCauses(err, { maxDepth?: number })` as a generator yielding each error in the chain. Default `maxDepth` is 32. Cycles MUST be detected via a `WeakSet` and terminate iteration without throwing. The same cycle-and-depth discipline SHALL apply to `toJSON` serialization: when traversal encounters a cycle OR exceeds `maxDepth`, the cause field is replaced with the `TruncatedCause` sentinel (see "TruncatedCause sentinel" requirement) rather than throwing or looping.
+
+**Verified by:** `src/causes/walk-causes.test.ts` and `src/conformance.spec-conformance.test.ts` (toJSON cycle + depth-cap scenarios).
+
+#### Scenario: Linear chain fully traversed
+
+- **WHEN** `a.cause = b; b.cause = c; c.cause = d`
+- **THEN** `Array.from(walkCauses(a))` returns `[a, b, c, d]`
+
+#### Scenario: Cycle terminates iteration
+
+- **WHEN** `a.cause = b; b.cause = a` and `walkCauses(a)` is consumed
+- **THEN** iteration yields `a` then `b` and ends (does not throw, does not loop forever)
+
+#### Scenario: Depth cap enforced
+
+- **WHEN** a chain of 100 errors is walked with `{ maxDepth: 10 }`
+- **THEN** exactly 10 errors are yielded
+
+#### Scenario: toJSON cycle yields TruncatedCause sentinel
+
+- **WHEN** `a.cause = b; b.cause = a` and `toJSON(a)` runs
+- **THEN** `result.cause.cause.code === "ERROR.CAUSE.TRUNCATED"` AND iteration does not loop forever
+
+### Requirement: Lossless wire serialization
+
+The package SHALL export `toJSON(err)` and `fromJSON(value)` producing a Zod-validated wire payload. `fromJSON` returns a `ReconstructedError` POJO carrying the `__suaveplanError: 1` discriminator — NOT a real `SuaveplanError` instance, since the base class is `abstract` and consumer-defined subclasses are not on the wire. Round-tripping a `SuaveplanError` subclass through JSON MUST preserve `code`, `message`, `context` (redactions applied), `timestamp`, `traceId`, `name`, and the cause chain (up to `maxDepth`). The binary form (`toBinary` / `fromBinary`) is a deterministic UTF-8 encoding of the canonicalised JSON form (no external encoder dep); both halves of a round-trip produce structurally identical output.
+
+**Verified by:** `src/serialize/serialize.test.ts` and `src/conformance.spec-conformance.test.ts` (discriminator round-trip scenario).
+
+#### Scenario: JSON round-trip preserves structural fields and discriminator
+
+- **WHEN** an error with `{ code, message, context, cause }` is serialized via `toJSON` and parsed back via `fromJSON`
+- **THEN** the reconstructed value carries `__suaveplanError === 1` AND every wire field (`code`, `message`, `context` post-redaction, `timestamp`, `traceId`, `name`, `cause`) is structurally equal to the original AND the result is NOT `instanceof SuaveplanError` (intentionally — base class is abstract)
+
+#### Scenario: Binary round-trip matches JSON round-trip
+
+- **WHEN** the same error is passed through `toBinary` / `fromBinary`
+- **THEN** the resulting reconstructed value is structurally equal to the JSON round-trip output
+
+#### Scenario: Zod rejects malformed wire payload
+
+- **WHEN** `fromJSON({ code: 123 })` is called (wrong type)
+- **THEN** it throws an error with `code === "ERROR.WIRE.MALFORMED"` AND `cause instanceof ZodError`
+
+### Requirement: Redaction at the serialization boundary
+
+The package SHALL export `markSensitive(value)` producing a tagged wrapper. During `toJSON` / `toBinary`, tagged values MUST be replaced with the literal string `"[REDACTED]"` AT ANY DEPTH within `err.context` — including values nested inside arrays and sub-objects. The redaction walk MUST be cycle-safe (a circular context graph terminates without throwing or looping). In-memory access to the original value via `err.context` is UNAFFECTED.
+
+**Verified by:** `src/redact/sensitive.test.ts`, `src/serialize/serialize.test.ts`, and `src/conformance.spec-conformance.test.ts` (deep + cycle-safe redaction scenarios).
+
+#### Scenario: Sensitive field redacted on the wire
+
+- **WHEN** `err.context.token = markSensitive("abc")` and `toJSON(err)` runs
+- **THEN** the serialized payload contains `context.token === "[REDACTED]"` (string)
+
+#### Scenario: Nested sensitive value redacted
+
+- **WHEN** `err.context.user = { profile: { token: markSensitive("abc") } }` and `toJSON(err)` runs
+- **THEN** `result.context.user.profile.token === "[REDACTED]"`
+
+#### Scenario: Sensitive value inside array redacted
+
+- **WHEN** `err.context.tokens = [markSensitive("a"), markSensitive("b")]` and `toJSON(err)` runs
+- **THEN** `result.context.tokens === ["[REDACTED]", "[REDACTED]"]`
+
+#### Scenario: Cyclic context terminates redaction
+
+- **WHEN** `err.context.self` is set to a cycle (`ctx.self = ctx`) and `toJSON(err)` runs
+- **THEN** redaction completes without throwing or looping (cycle short-circuits via `WeakSet`)
+
+#### Scenario: In-memory value remains accessible
+
+- **WHEN** `err.context.token = markSensitive("abc")` (unserialized)
+- **THEN** `unwrapSensitive(err.context.token) === "abc"`
+
+## ADDED Requirements
+
+### Requirement: TruncatedCause sentinel
+
+When `toJSON` encounters either (a) a cause-chain depth that exceeds `maxDepth` OR (b) an already-seen object (cycle), the cause field SHALL be replaced with a sentinel `WireError` of shape `{ __suaveplanError: 1, code: "ERROR.CAUSE.TRUNCATED", name: "TruncatedCause", message: "[cause chain truncated]", timestamp: 0 }`. The sentinel is structurally a valid `WireError` (passes Zod validation) and is therefore safely consumable by `fromJSON` downstream. The sentinel MUST NOT introduce a real `Error` throw; truncation is a non-fatal terminal event in the chain.
+
+**Verified by:** `src/conformance.spec-conformance.test.ts` (depth + cycle sentinel scenarios) and `src/serialize/serialize.test.ts`.
+
+#### Scenario: Depth-cap emits sentinel
+
+- **WHEN** `toJSON(err, { maxDepth: 1 })` runs on an error with `cause.cause.cause` of depth 3
+- **THEN** the chain at the cap position contains the `TruncatedCause` sentinel AND `result.cause.cause.code === "ERROR.CAUSE.TRUNCATED"`
+
+#### Scenario: Cycle emits sentinel
+
+- **WHEN** `toJSON(a)` runs on `a.cause = b; b.cause = a` (cycle)
+- **THEN** the chain terminates at the cycle with the sentinel AND no infinite loop occurs
+
+#### Scenario: Sentinel survives round-trip
+
+- **WHEN** a `toJSON` output containing a `TruncatedCause` sentinel is passed back through `fromJSON`
+- **THEN** the reconstructed value carries the sentinel intact (`code === "ERROR.CAUSE.TRUNCATED"`, `name === "TruncatedCause"`) without throwing `WIRE.MALFORMED`
+
+### Requirement: Wire format version discriminator
+
+The wire payload SHALL carry a `__suaveplanError: 1` discriminator literal validated by Zod's `z.literal(1)`. This identifies the payload as a `@suaveplan/error` wire envelope and pins the format version. `WIRE_VERSION` is the single source-of-truth constant in `src/constants/index.ts`. `fromJSON` MUST reject payloads where `__suaveplanError` is missing OR not equal to `WIRE_VERSION` with `code === "ERROR.WIRE.MALFORMED"` (Zod-driven). When `WIRE_VERSION` is bumped (future), payload migration is the consumer's responsibility — there is no implicit version negotiation in this package.
+
+**Verified by:** `src/serialize/wire.schemas.ts` (Zod literal), `src/serialize/serialize.test.ts`, and `src/conformance.spec-conformance.test.ts` (discriminator scenarios).
+
+#### Scenario: Discriminator preserved through round-trip
+
+- **WHEN** an error is passed through `toJSON` then `fromJSON`
+- **THEN** the reconstructed value has `__suaveplanError === 1`
+
+#### Scenario: Missing discriminator rejected
+
+- **WHEN** `fromJSON({ code: "X.Y.Z", message: "m", timestamp: 0, name: "E" })` runs (no `__suaveplanError`)
+- **THEN** it throws with `code === "ERROR.WIRE.MALFORMED"`
+
+#### Scenario: Wrong discriminator rejected
+
+- **WHEN** `fromJSON({ __suaveplanError: 2, ...rest })` runs
+- **THEN** it throws with `code === "ERROR.WIRE.MALFORMED"` (Zod literal mismatch)