fix: emit structured JSON from Codex context hooks#87
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Codex classifies hook stdout beginning with `[` or `{` as attempted JSON and
parses it. Mnemon's SessionStart (prime) and UserPromptSubmit hooks emit context
beginning with `[mnemon]`, so Codex tries to parse it, fails, and reports
`hook returned invalid ... JSON output` on every session start and prompt.
Move the existing context into Codex's documented
`hookSpecificOutput.additionalContext` envelope:
- user_prompt.sh: emit the reminder as a static UserPromptSubmit object.
- prime.sh: pipe the existing status/warning/guide output through
`python3 json.dumps` into a SessionStart object (python3 is already required by
the sibling stop.sh). Existing context and MNEMON_DATA_DIR path resolution are
unchanged. Guide bytes are read via sys.stdin.buffer and decoded with
errors="replace", so invalid UTF-8 in the guide can never crash the hook or
emit lone surrogates that strict JSON parsers reject.
stop.sh already emitted valid JSON and is untouched.
Add internal/setup/assets/codex_hooks_test.go, which executes the embedded hook
byte slices and asserts their external JSON contract: exact additionalContext
equality across the missing-binary, stats, empty-status, MNEMON_DATA_DIR
override, and legacy-fallback cases, plus an invalid-UTF-8 case asserting the
hook exits zero and emits no lone-surrogate escapes. The tests fail on the
pre-patch hooks and pass with this change.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Codex's hook-output parser treats any hook stdout beginning with
[or{as an attempted JSON object and rejects it if it isn't valid hook JSON (codex-rs/hooks/src/engine/output_parser.rslooks_like_json+session_start.rs). Mnemon's Codex SessionStart (prime) and UserPromptSubmit hooks print context beginning with[mnemon] …, so Codex fails to parse them on every session start and prompt, and the memory context can be dropped.This aligns those two hooks with Codex's documented hook-output contract by wrapping their existing output in
hookSpecificOutput.additionalContext— the context text is unchanged:user_prompt.sh: emit the reminder as a staticUserPromptSubmitobject.prime.sh: pipe the existing status/warning/guide output throughpython3 json.dumps(reading stdin as bytes and decoding UTF-8 witherrors="replace", so arbitrary guide bytes can't break the JSON) into aSessionStartobject. Existing context andMNEMON_DATA_DIRpath resolution are unchanged.python3is already required by the siblingstop.sh, so no new dependency.stop.shalready emits a valid JSON object, so it never triggered this parse failure — left untouched.Adds
internal/setup/assets/codex_hooks_test.go, which executes the embedded hook byte slices and asserts their external JSON contract (missing-binary, stats, empty-status,MNEMON_DATA_DIRoverride, legacy fallback, and invalid-UTF-8 guide). The tests fail on the pre-patch hooks and pass with this change.Closes #86