feat(plugin): WASM hook registration and execution (#444)

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Summary

• Add hooks() export discovery during LoadModule — parses JSON array of hook names, validates format, fails loud on invalid data
• Implement CallHook(name, payload) — marshals JSON envelope {"event":"<name>","payload":<data>}, dispatches via existing callStringFilter ABI, parses JSON response
• Implement RegisteredHookDetails() (HookDetailer interface) — returns HookRegistration with default priority 50 for each discovered hook
• Add "hooks" to wasmRuntimeExports reserved set so hook discovery export isn't treated as a filter
• Rebuild compiled.wasm with hooks()/hook() exports (WAT source included)
• Add bad-hooks-export.wasm fixture (invalid JSON from hooks()) and wasm-malformed-hook-response.wasm fixture (non-JSON from hook())

Closes #444

Test plan

• All 176 plugin tests pass (0 failed, 0 pending, 0 skipped)
• 10 issue spec(plugin): WASM hook registration and execution tests #444 spec tests pass: CallHook type assertion, hook discovery, HookRegistry bridging, JSON envelope, priority 50, (0,0) error, invalid hooks JSON, malformed response
• Existing WASM filter/ABI/sandbox tests still pass with rebuilt compiled.wasm
• Full test suite: no regressions outside pre-existing Goldmark templateTags: empty <p></p> generated around template tag blocks #564 content tests

🤖 Generated with Claude Code

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Pull request overview

Adds WASM plugin hook support to the Tier 2 WASMRuntime so WASM modules can (1) declare which lifecycle hooks they implement and (2) be invoked via the existing WASM string ABI, enabling integration with the HookRegistry alongside QuickJS and Node runtimes.

Changes:

• Discover hook names from a hooks() WASM export during LoadModule() and expose them via RegisteredHooks() / RegisteredHookDetails() (default priority 50).
• Implement CallHook(name, payload) for WASM by JSON-marshaling an {event, payload} envelope, dispatching through the existing (ptr,len)->(ptr,len) ABI, and JSON-parsing the response.
• Update/add WASM fixtures (compiled.*, bad-hooks-export.*, wasm-malformed-hook-response.*) to cover hook discovery and malformed response cases.

Reviewed changes

Copilot reviewed 4 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
internal/plugin/wasm.go	Implements WASM hook discovery/registration details and CallHook, and reserves "hooks" in the export set.
internal/plugin/testdata/single-files/compiled.wat	WAT source for the rebuilt compiled WASM fixture including hooks()/hook() exports.
internal/plugin/testdata/single-files/compiled.wasm	Rebuilt WASM fixture binary with hooks()/hook() exports for hook tests.
internal/plugin/testdata/single-files/bad-hooks-export.wat	WAT source for a fixture returning invalid JSON from hooks().
internal/plugin/testdata/single-files/bad-hooks-export.wasm	Fixture binary returning invalid JSON from hooks().
internal/plugin/testdata/single-files/wasm-malformed-hook-response.wat	WAT source for a fixture returning non-JSON bytes from hook().
internal/plugin/testdata/single-files/wasm-malformed-hook-response.wasm	Fixture binary returning non-JSON bytes from hook().

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Code Review — PR #570 (Review #1)

9/9 reviewers returned | Verdict: Ready to merge

Findings

#1 P2 safe_auto — RegisteredHooks(), RegisteredHookDetails(), CallHook(), discoverHooks() lack doc comments. Every other exported method on WASMRuntime has one. The old RegisteredHooks comment was removed but not replaced. RegisteredHookDetails hardcodes Priority 50 with no comment explaining the ABI limitation.

#2 P2 safe_auto — hookNames not cleared in Close(). If LoadModule is called after a prior successful load, Close() runs but hookNames survives. If the second LoadModule fails before discoverHooks (e.g., at CompileModule), RegisteredHooks() returns stale names from the defunct module.

#3 P2 safe_auto — discoverHooks has two silent failure paths: (a) len(results) < 2 returns nil silently — callStringFilter errors on wrong result count, but discoverHooks doesn't. (b) ptr == 0 && length == 0 treated as "no hooks" but (0,0) is the ABI error convention. A hooks() that fails internally returns (0,0) per convention, but discoverHooks doesn't check last_error(). The module's hooks silently disappear.

#4 P2 safe_auto — No validation of hook names from WASM module. discoverHooks accepts any strings from the JSON array. Empty strings would be registered and routed through the hook registry. A filter for empty strings would be defensive.

#5 P2 advisory — Cross-runtime CallHook contract: QuickJS returns (payload, nil) for unregistered hooks, WASM errors via (0,0). The spec test at line 731 codifies the error behavior. The registry gates dispatch, so this only matters for direct callers. Intentional but undocumented.

#6 P2 advisory, pre-existing — Bump allocator exhaustion: monotonic alloc never resets, accumulates across per-page hook/filter calls. ~100 pages with moderate HTML can exhaust 64KB linear memory.

#7 P2 advisory, pre-existing — RunWithTimeout abandoned goroutines can race with subsequent WASM calls on the same bump allocator. Pre-existing — applies to all WASM operations.

#8 P3 safe_auto — CallHook returns "wasm module not loaded" while CallExport returns "wasm module not loaded — call LoadModule first". Minor inconsistency.

#9 P3 advisory — WASM hooks lack scope/priority metadata in ABI. hooks() returns only names. Hardcoded priority 50, no scope filtering. By design for ABI simplicity.

#10 P3 advisory — JSON envelope ABI: CallHook wraps input in {"event", "payload"} but doesn't unwrap output. compiled.wat echoes the full envelope. Real plugins must return only the processed payload. Contract should be documented.

#11 P3 advisory, pre-existing — ExportedFunction("alloc"), Memory(), ExportedFunction("hook") looked up per call. wazero returns O(1) from internal map, so minimal overhead. Caching would be consistent with existing exports caching.

Testing Gaps (advisory)

1. CallHook happy-path test asserts only NotNil — doesn't verify result content
2. r.mod == nil path in CallHook has no test
3. Module without hook() export path has no test
4. discoverHooks hooksFn==nil branch not tested via module load
5. discoverHooks defensive branches (arity, (0,0), mem==nil, Read fail) all untested
6. No concurrent access test, no nil payload test, no round-trip payload structure test

Residual Risks

1. WASM bump allocator never resets — alloc calls accumulate. Pre-existing.
2. No timeout on WASM calls — context.Background() with no deadline throughout. Pre-existing.
3. No mutex on WASMRuntime — concurrent access would race hookNames, mod, exports.

Recalibration Notes

• 2 adversarial P1s recalibrated: ADV-001 (cross-runtime contract → P2, spec-intentional), ADV-002 (timeout race → P2 pre-existing)
• 1 adversarial finding dismissed: ADV-003 (mem.Read alias → conf 30, self-refuted)
• 2 maintainability P1s recalibrated: MAINT-001 (merged with ADV-001 → P2), MAINT-002 (doc comments → P2)
• 5 testing findings demoted to testing gaps (implementation PR, spec tests immutable)
• 4 cross-reviewer merges (hookNames/Close, CallHook contract, discoverHooks silent failures, JSON envelope)

Run artifact: 20260511-c5d73f28

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Response to Review #1

All Copilot threads resolved. Fixes pushed in f0003ae.

Fixed (safe_auto)

#1 Missing doc comments — Added doc comments to RegisteredHooks, RegisteredHookDetails, CallHook, and discoverHooks. RegisteredHookDetails comment now documents the ABI limitation for priority 50.

#2 Stale hookNames on Close/reload — hookNames cleared in both Close() and at the top of LoadModule().

#3 Silent failure paths in discoverHooks — Two changes: (a) len(results) < 2 now returns an error instead of silent nil. (b) (0,0) return now checks last_error() per the ABI error convention before treating as "no hooks."

#4 Empty hook name validation — discoverHooks now filters empty strings and deduplicates via seen-set.

#8 Inconsistent error message — CallHook now returns "wasm module not loaded — call LoadModule first" matching CallExport.

Additionally fixed (from Copilot threads)

Validate hook() export — discoverHooks now errors when hooks() declares hook names but the module has no hook() export. Prevents registering hooks that would always fail at execution time.

Acknowledged (advisory, no action)

#5 Cross-runtime CallHook contract — Intentional. WASM delegates unknown events to the module (which returns (0,0) per ABI), QuickJS returns passthrough. The registry gates dispatch so this only matters for direct callers. Spec test at line 731 codifies the WASM behavior.

#6-7 Bump allocator exhaustion / RunWithTimeout races — Pre-existing, applies to all WASM operations.

#9 No scope/priority in WASM ABI — By design for ABI simplicity. Documented in RegisteredHookDetails comment.

#10 JSON envelope contract — The envelope wrapping is the host-side contract. WASM modules receive {"event":"<name>","payload":<data>} and return the processed payload. The echo behavior in compiled.wat is a test fixture simplification.

#11 Per-call function lookups — wazero's ExportedFunction is O(1) map lookup. Caching would be consistent but negligible gain.

Testing gaps

Acknowledged. These are advisory — spec tests are immutable and the implementation tests cover the contract.