fix(capy): the launch environment is sourced from a 0600 file and no skill fence may print the environment (GSTA-104)

During GSTA-96's unattended /ship on #3425, the Step 14.5 docs-audit child
re-typed the GSTACK_LAUNCH assignments as `export $(...)`; the substitution
came back empty, the bare `export` printed the whole environment, and three
API key values landed in its tool output.

- bin/gstack-capy-install writes the assignments to <verdict>.env (mode 0600,
  idempotent PATH prepend) and prints GSTACK_LAUNCH_FILE: <path>.
- ship Step 14.5 prompt, document-release's spawned note, autoplan/DRIVER.md
  and gstack-skill-start's capy-asks block say: source the file; never
  export $(...), env, printenv or bare set in a tool fence.
- test/launch-env-echo-ratchet.test.ts greps every generated SKILL.md,
  sections, DRIVER.md, the Capy skill and bin/ shell helpers, with negative
  controls under test/fixtures/launch-env-echo/.
- lib/redact-engine.ts: env.value (HIGH) finds the value of any *_KEY,
  *_TOKEN, *_SECRET, *_PASSWORD variable in the writer's environment, so a
  leaked value cannot reach a PR body, receipt, report or Drive file.
- scripts/lib/shard-engine.ts scrubs the Capy launch markers from shard
  environments (GSTA-99's finding).

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

scripts/lib/shard-engine.ts

@@ -582,9 +582,18 @@ export function createShardSandbox(
     ...baseEnv, TMPDIR: tmp, TEMP: tmp, TMP: tmp,
     CHROMIUM_PROFILE: path.join(stateDir, 'chromium-profile'),
   };
+  for (const name of CAPY_LAUNCH_MARKERS) delete env[name];
   return { stateDir, tmp, env };
 }
 
+/**
+ * The Capy installer's `GSTACK_LAUNCH` markers. A lane started from a shell
+ * that sourced the launch file would hand them to every product-under-test
+ * child a shard spawns, so fixtures would see an unattended Capy session they
+ * never set up (GSTA-99); each fixture sets its own session kind.
+ */
+export const CAPY_LAUNCH_MARKERS = ['GSTACK_SESSION_KIND', 'GSTACK_CAPY', 'GSTACK_EPHEMERAL', 'GSTACK_INSTALL_VERDICT'] as const;
+
 /**
  * Asynchronous best-effort backstop removal: a SIGKILLed shard can leave a
  * full git workspace plus a Chromium profile, and a synchronous recursive