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Tom Boucher 96a82bbffb enhance(#3245 ): report the detected host runtime in init (#3307 )

* test(#3245): failing-first coverage for host runtime detection in init

Locks the behavior epic #2313 Phase 5 must produce before any of it exists: init reports the detected host, explicit GSD_RUNTIME and config runtime still outrank detection, non-Codex sessions are untouched, and nothing is ever written to shared defaults (#2297).

* enhance(#3245): report the detected host runtime in init

init reported agent_runtime: claude inside a Codex session, and resolved agents_dir to the Claude agents root with agents_installed: true — a spuriously healthy triple. Runtime identity was only ever read from GSD_RUNTIME or an explicit runtime in .planning/config.json.

Adds a detection rung beneath both explicit sources, in a new pure module. Codex is identified from its own documented session environment (CODEX_SANDBOX / CODEX_SANDBOX_NETWORK_DISABLED), else an explicitly exported CODEX_HOME whose config.toml exists. The default ~/.codex is never probed: that file exists on every machine that has run Codex, so probing it would misreport other runtimes' sessions.

resolveRuntime keeps its exact contract and all 71 dependents, including formatGsdSlash command-style emission; only withProjectRoot consumes the new rung. Nothing is written on any path (#2297). Explicit config still wins (#2517).

* fix(#3245): make the parity guard real and single-source the marker

Four independent review passes found the generative-fix-divergence guard was vacuous: it asserted agreement at the one input where inferPreferredRuntime and detectHostRuntime do not differ, so it could not fail. It now pins the actual divergence point (CODEX_HOME set, config.toml absent) and records that the asymmetry is deliberate.

The config.toml marker is now single-sourced from update-context.cts and imported, rather than carried independently by two surfaces. tests/helpers.cjs now scrubs CODEX_SANDBOX and CODEX_SANDBOX_NETWORK_DISABLED: GSD reads them, so an ambient Codex session would otherwise make the non-codex control test fail non-deterministically.

Also: detection is throw-safe end to end rather than only around the fs probe; the Windows-join test is replaced with one that can actually fail (trailing-separator, catches hand-rolled concatenation); the #2297 no-write proof now wraps resolveReportedRuntime, the function that ships, across all three ladder outcomes.

* chore(#3245): backfill changeset pr number

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Co-authored-by: sim <sim@local>

2026-08-10 09:48:26 -04:00

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How to control which host runtime GSD reports

Goal: Make agent_runtime — the runtime GSD reports it is running under, and the one it checks for installed agents — say what you actually want, and know why it says what it says.

Prerequisites: A project with a .planning/ directory. Read the current answer with:

node gsd-tools.cjs init plan-phase 1 --raw

The JSON carries agent_runtime, plus the agents_dir / agents_installed / missing_agents triple derived from it. For the config key itself, see runtime.

The ladder, in order

GSD answers "which runtime am I?" from the first of these that produces a value:

#	Source	Set it by	Wins over
1	`GSD_RUNTIME` environment variable	`GSD_RUNTIME=opencode` in the environment	everything below
2	`runtime` in `.planning/config.json`	`"runtime": "codex"`	detection and the default
3	Host detection (added in v1.11)	nothing — it is automatic	the default only
4	Default	—	— (`claude`)

Rungs 1 and 2 are explicit — you stated an intent, and GSD does not second-guess it. Rung 3 only ever runs when both are unset. This is what preserves the behavior of every existing config: if you have ever set runtime, nothing about your setup changes.

What detection actually looks at

Detection answers a narrow question — is this process running inside a Codex session? — and only from signals Codex itself documents.

Signal	Where it comes from	Why it is trusted
`CODEX_SANDBOX` is set and non-empty	Codex injects it into child processes it spawns via Seatbelt	Documented in Codex's own `AGENTS.md`; present in exactly the processes Codex runs, which is where GSD runs
`CODEX_SANDBOX_NETWORK_DISABLED` is set and non-empty	Codex injects it when running the shell tool with the network sandbox on	same source
`CODEX_HOME` is set and `$CODEX_HOME/config.toml` exists	you exported it	Exporting `CODEX_HOME` is you designating a Codex state root; the `config.toml` check confirms the directory is a real one

Anything else — no signal — means no detection, and rung 4 applies.

The two questions this page exists for

"I'm in a Codex session and it still says `claude`"

Work down the ladder:

Check	What to do
Is `GSD_RUNTIME` set to something else?	`echo $GSD_RUNTIME` — it outranks everything. Unset it, or set it to `codex`.
Does `.planning/config.json` have a `runtime`?	An explicit `"runtime": "claude"` wins over detection, by design. Change it or remove the key.
Is your Codex sandbox off?	With `sandbox_mode = "danger-full-access"`, Codex sets neither sandbox variable, so there is nothing for GSD to detect. This is the most common cause.
Still nothing?	Set it explicitly. Detection is a convenience, not a contract — `"runtime": "codex"` in `.planning/config.json` is the supported, permanent answer.

Detection is deliberately conservative: when it cannot tell, it reports the old default rather than guessing. A wrong agent_runtime sends GSD looking for agents in the wrong directory, so silence is the safer failure.

"It says `codex` and I am not using Codex"

One cause, and it is benign:

CODEX_HOME is exported in your shell profile, and $CODEX_HOME/config.toml exists.

GSD treats an explicitly-exported CODEX_HOME as you designating a Codex root. If you keep it exported globally but work in another runtime, pin the runtime for that project:

{ "runtime": "claude" }

in .planning/config.json. Rung 2 outranks detection, so this settles it permanently.

Note what is not a cause: simply having Codex installed. GSD never probes the default ~/.codex/config.toml. That file exists on every machine that has ever run Codex, so treating it as a signal would misreport every other runtime's sessions — which is precisely why the check requires you to have exported CODEX_HOME yourself.

What this does not change

Detection moves the reported runtime and the agent-installation check that hangs off it. It deliberately does not touch:

Model resolution. Runtime-aware tier resolution still reads the explicit runtime config key only. A detected-Codex session does not gain or lose model pins — see Runtime-aware profiles and ADR-2313.
Slash-command style. GSD still emits /gsd-<cmd> unless the runtime was set explicitly; a detected-Codex session does not switch to the $gsd-<cmd> shell-var form. Set runtime explicitly if you want that.
Any file. Detection reads environment variables and checks for one file's existence. It never writes ~/.gsd/defaults.json, never edits .planning/config.json, and never shells out.

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