docs: AGENTS.md + evidence-backed scaffold (state, trials, decisions, handoff)

- AGENTS.md operating rules incl. Gitea SSH port-2222 note + known_hosts incident
- CURRENT_STATE / TODO / CHANGELOG / TRIALS
- trials: endpoint-key pairing; config-merge safety matrix 14/14 (verify.sh + output)
- docs: DECISIONS (mcode 0.6.12 bundle facts, digest-pinned), FEATURE-MATRIX, PROJECT-HANDOFF
- handoffs: TEMPLATE + 2026-10-19 initial-install record

CHANGELOG.md

@@ -0,0 +1,29 @@
+# CHANGELOG
+
+Reverse-chronological. Meaningful changes only; each entry points at evidence.
+
+## 2026-10-19 — initial release: segment, installer, docs scaffold
+
+- `zai-usage.sh` — statusline custom command: Aygea-palette `🔥 <pct>% · <clock>(<remaining>)`
+  segment; SecretVault-first auth (`secretvault run`, key never in argv) with
+  `~/.secretvault/credential.json` fallback; cache-shared with the Claude Aygea
+  statusline (`~/.cache/aygea-sl/quota.json`, schema `{pct, reset_iso, ts}`);
+  detached flock-guarded background refresh (no cron/systemd); always exit 0;
+  GNU/BSD date + flock/setsid fallbacks for macOS.
+- `install.sh` — self-extracting installer (`curl | bash`): installs to
+  `~/.local/bin/mcode-zai-usage`, checks SecretVault presence (never prints the secret),
+  surgically merges the `tui:` section into `~/.minimax/config.yaml` (atomic
+  temp+fsync+rename, 0600, timestamped backup before change, duplicate-structure
+  refusal, byte-identical outside the tui block), primes the cache, `--uninstall` mode.
+- Fixed during development: EXIT trap referencing function-local vars under `set -u`;
+  uninstall mode-name mismatch (`uninstall` vs `remove`); TOP regex never capturing the
+  key name (false "duplicate top-level keys" refusals); embedded-copy forward reference
+  (0-byte installs in piped mode); double-newline on re-embed.
+- Config merge hardening per user request: atomicity + previous-entry checks + format
+  safety (see `docs/DECISIONS.md` D5, trial `config-merge-safety-2026-10-19`).
+- Installed on this machine (backup `~/.minimax/config.yaml.bak.20261019-231642`),
+  cache primed `🔥 1%`; pushed to `git.itsaygea.com/admin/mcode-sl` (`main`).
+- SSH: corrected Gitea-on-2222 setup; removed wrong port-22 host keys from
+  `~/.ssh/known_hosts` (details in `AGENTS.md` → "SSH to Gitea").
+- Docs scaffold: AGENTS/CURRENT_STATE/TODO/CHANGELOG/TRIALS + `docs/`, `trials/`,
+  `handoffs/`, `tooling/`, `evidence/`.