fix(runtime): mint storage-safe retained session identities

[drewstone]

Retained child dispatches fail before model startup because Runtime generates session IDs containing colons and percent escapes. The Tangle sidecar rejects those IDs on both cached-turn lookup and workspace resolution. Mint deterministic retained-session-<sha256> and retained-execution-<sha256> coordinates that satisfy the existing filesystem contract.

Recovery uses the identities recorded in the original admission. It still validates the request digest and explicit identity conflicts. Interactive recovery accepts exact historical readable or hashed coordinates, and malformed recorded identities fail before provider work. Existing run records and filesystem validation remain unchanged.

Validation:

• Reproduced HTTP 400 INVALID_SESSION_ID through the real sidecar messages route with the captured Runtime ID; the patched generator's ID returns the expected 204 cache miss and passes native workspace resolution. No model invocation was made.
• Full suite: 3,681 passed, 11 skipped. Final targeted recovery and Sandbox suites: 108 passed, including historical replay and malformed-intent regressions.
• Lint, source/examples typecheck, packed-package exports, edge module loading, and docs freshness pass.
• Independent adversarial review found and verified the fix for malformed recorded IDs; no remaining blocking findings.

Prepares Runtime 0.208.1. The active research process remains on its original dependency cohort; this change does not modify or restart it.

[drewstone]

Concurrent-session coordination: the named-resource work for #1041 is isolated on feat/resource-budget-release in /tmp/rt-resources-final-20260909 and reserves Runtime 0.209.0.
It includes the merged #1154 baseline, exact integer resource accounting, production Router receipt propagation, and retained live Sandbox terminal evidence.

I will let this 0.208.1 release finish before integrating current main and tagging 0.209.0.
No changes to this PR's retained identity files are planned in my branch.
An accompanying Eval 0.180.0 reader change is in progress; my Runtime PR will also own the resulting agent-bench dependency update.