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>

docs/capy-install.md

@@ -330,8 +330,23 @@ Every successful run, `--check` included, prints before the trailer:
 ```
 GSTACK_LAUNCH: PATH=<dir>:$PATH GSTACK_SESSION_KIND=unattended GSTACK_STATE_ROOT=<path> GSTACK_EPHEMERAL=1 GSTACK_CAPY=1 GSTACK_INSTALL_VERDICT=<file>
 GSTACK_LAUNCH_PATH: <dir>
+GSTACK_LAUNCH_FILE: <verdict file without .json>.env
 ```
 
+`GSTACK_LAUNCH_FILE` names the same assignments as a sourceable script (mode
+0600, beside the verdict under the state root; the PATH prepend is idempotent).
+`. <that file>` at the start of a shell applies them without ever printing them,
+which is the only way to hand them to a child agent: pass the path, never the
+values. None of the assignments is a secret, but during GSTA-96's unattended
+/ship a docs-audit child re-typed them as `export $(...)`; the substitution came
+back empty, the bare `export` printed the whole environment, and three API key
+values landed in its tool output. Never `export $(...)`, `env`, `printenv`, a
+bare `set` or a bare `export` in a tool fence (`test/launch-env-echo-ratchet.test.ts`
+keeps them out of every skill fence and shell helper), and the redaction
+engine now refuses the VALUE of any `*_KEY`, `*_TOKEN`, `*_SECRET` or
+`*_PASSWORD` variable in the writer's environment (`env.value`, HIGH), so a
+leaked value cannot reach a PR body, receipt, report or Drive file.
+
 `PATH=<dir>:$PATH` and `GSTACK_LAUNCH_PATH` appear only when the certified Bun,
 or the project's resolved Node, is not first on PATH (older Capy images ship
 `/usr/local/bin/bun` 1.3.14; 57 gstack commands start with `#!/usr/bin/env bun`).