docs: web-tab egress guard, capability revocation and referrer policy

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WKtW48T1UjAaecHAJxKobE

CLAUDE.md

@@ -268,7 +268,7 @@ Codeman is a Claude Code session manager with web interface and autonomous Ralph
 
 **Cross-session search**: `GET /api/search` federates an in-memory search over session metadata, run-summary events, and attachment-history entries. The pure core `searchSources()` does substring matching with hard per-type caps: **no regex (so no ReDoS) and no filesystem reads (so no traversal)**. The server-private `externalPath` is never read. PAST sessions (#261) come from `session-history-index.ts`, a capped snapshot of the unified list filled **outside** the request path (`/api/sessions/unified` publishes it; a stale one is rebuilt fire-and-forget), that indirection is what keeps the no-fs property. ⚠️ The snapshot is stored UNSCOPED with a per-row owner and MUST be re-filtered through `canAccessOwned()` on read; history rows carry `jumpTo.kind:'resume-session'`, since a closed session has no tab to select. → [architecture-invariants#cross-session-search](docs/architecture-invariants.md#cross-session-search)
 
-**Web tabs** (dashboard URLs as tabs): a saved URL renders as a tab beside agent sessions. **NOT a `SessionMode` of its own** (no PTY, no tmux, no respawn), same reasoning that keeps Docker/remote-SSH as case overlays. Dashboards are **proxied through Codeman's own origin** by default, because a direct iframe fails three ways at once: prod is HTTPS so `http://` targets are blocked as mixed content, many dashboards send `X-Frame-Options: DENY`, and our own `default-src 'self'` CSP blocks cross-origin frames. Proxying leaves the prod CSP unchanged (`/webview/...` is `'self'`). ⚠️ The proxy is **NOT an API surface**: it authenticates on an in-memory capability in the path and is correspondingly exempt from the cookie + Origin checks; that exemption is fenced to safe methods and non-`/api` paths and is pinned by `test/webview-auth-exemption.test.ts`. ⚠️ Iframes omit `allow-same-origin` unless a dashboard is explicitly marked `trusted`, and `Authorization`/`codeman_session` are stripped upstream in **both** modes so `CODEMAN_PASSWORD` cannot leak. ⚠️ A sandboxed frame is **opaque-origin**, which breaks two things `curl` can never reproduce: its runtime-built root-absolute URLs escape `<base>` (fixed by an injected `runtimeUrlShim()`), and its same-host `fetch`/XHR are CORS-checked with `Origin: null` (fixed by `buildProxyCorsHeaders()` plus exempting the proxy from the global `OPTIONS`-204 short-circuit in `registerSecurityHeaders`). Both present as the dashboard's own "Failed to fetch" while the page renders fine. → [architecture-invariants#web-tabs](docs/architecture-invariants.md#web-tabs), `docs/web-tabs.md`
+**Web tabs** (dashboard URLs as tabs): a saved URL renders as a tab beside agent sessions. **NOT a `SessionMode` of its own** (no PTY, no tmux, no respawn), same reasoning that keeps Docker/remote-SSH as case overlays. Dashboards are **proxied through Codeman's own origin** by default, because a direct iframe fails three ways at once: prod is HTTPS so `http://` targets are blocked as mixed content, many dashboards send `X-Frame-Options: DENY`, and our own `default-src 'self'` CSP blocks cross-origin frames. Proxying leaves the prod CSP unchanged (`/webview/...` is `'self'`). ⚠️ The proxy is **NOT an API surface**: it authenticates on an in-memory capability in the path and is correspondingly exempt from the cookie + Origin checks; that exemption is fenced to safe methods and non-`/api` paths and is pinned by `test/webview-auth-exemption.test.ts`. ⚠️ Iframes omit `allow-same-origin` unless a dashboard is explicitly marked `trusted`, and `Authorization`/`codeman_session` are stripped upstream in **both** modes so `CODEMAN_PASSWORD` cannot leak. ⚠️ A sandboxed frame is **opaque-origin**, which breaks two things `curl` can never reproduce: its runtime-built root-absolute URLs escape `<base>` (fixed by an injected `runtimeUrlShim()`), and its same-host `fetch`/XHR are CORS-checked with `Origin: null` (fixed by `buildProxyCorsHeaders()` plus exempting the proxy from the global `OPTIONS`-204 short-circuit in `registerSecurityHeaders`). Both present as the dashboard's own "Failed to fetch" while the page renders fine. ⚠️ **Egress guard**: link-local and cloud-metadata targets (`169.254.0.0/16`, `fe80::/10`, `fd00:ec2::254`, the Azure/Alibaba fixed addresses, `metadata.google.internal`) are refused at save time AND on the RESOLVED address at connect time (`webview-egress-policy.ts`, pure, plus `webview-egress.ts`: a `lookup` hook on the undici Agent behind `webviewFetch()` and on the `ws` client). An IP literal never reaches a lookup hook (`net.connect` skips DNS for it), so the synchronous hostname check at each connect site is NOT redundant. Loopback and RFC1918 stay allowed on purpose: a `localhost` Grafana is the feature. The proxy uses the `undici` PACKAGE's own `fetch` + `Agent`, never Node's global fetch with a foreign dispatcher (Node bundles its own copy; a protocol mismatch fails silently). Capabilities are revoked on logout / admin logout / user deletion (`revokeOwner`, which had NO caller for two releases while its docstring said otherwise), and proxied responses carry `Referrer-Policy: same-origin` so a dashboard cannot hand the capability-bearing URL to a third party. → [architecture-invariants#web-tabs](docs/architecture-invariants.md#web-tabs), `docs/web-tabs.md`
 
 **Multi-user mode** (opt-in `--multiuser` / `CODEMAN_MULTIUSER=1`, OFF by default): named users with scrypt-hashed passwords in `~/.codeman/users.json`. Gated everywhere by `isMultiUserMode()`; when OFF, behavior is byte-identical to single-user because every scoping helper short-circuits. ⚠️ **Not a security boundary at the agent layer**: every session still runs as the SAME OS account. This separates WORKSPACES; it does not sandbox users (Docker cases are the isolation story). Ownership threads through `Session.owner` and is enforced in `findSessionOrFail`, list endpoints, SSE routing (fail-closed), WS, search, and file-preview. → [architecture-invariants#multi-user-mode](docs/architecture-invariants.md#multi-user-mode), `docs/multi-user-plan.md`