fix(mcp): keep injected agent context on summaries

[ScriptedAlchemy]

Summary

• guard-the-context-window: stop the agent-facing defaults that put raw payloads back into the prompt.
• Merged latest feat: TraceDecay V2 delivery (PR8–PR13) + daemon performance, memory, and reliability overhaul #707 tip 3e6167b265639c17b7d1c174cd3b7baa3116adae into this branch (f88f92659f). Conflicts were only the compile-unblock copies of tip fixes; tip versions were kept.
• tracedecay_status matches the CLI compact contract. tracedecay_skill_view returns support-file summaries unless include_support_files=true. Truncated responses no longer tell the model to rejoin the stored body. Session steering builders enforce their budgets.

Does not merge #707 into master. Targets the #707 tip only.

Merge

• Tip SHA merged: 3e6167b265639c17b7d1c174cd3b7baa3116adae (test(code-index): re-pin partitioned codec onto extractor.rust.v8)
• Merge commit: f88f92659f1c12f18b58aa64b43689da15cab072
• Conflicts:
  • branch_publication.rs: kept the tip's typed NotApplicable → CODE_INDEX_IDENTITY_MISMATCH (non-retryable). Did not keep the earlier compile-only arm that treated it as queued.
  • publication_store.rs: kept the tip's non-enumerated reuse comment (reused_count / reused_digest; per-chunk Reused rows are ExtraChunkReceipt).

Motivation

The context window is finite. Review of PR #707 through guard-the-context-window found agent-facing surfaces that either dump raw data into the main prompt or instruct the model to reassemble it.

Changes

• tracedecay_status defaults the expensive sections off. Opt in for the full diagnostic list, storage health, session ingest, or Git staleness.
• tracedecay_skill_view no longer inlines support-file bytes by default. Path and byte_len summaries stay.
• Truncation recovery text and tracedecay_retrieve tell the model to use the preview and request one omitted span, not concatenate every page.
• Cursor/Codex session-context builders cap caller-supplied freshness text and enforce the documented budgets.
• Regression test keeps the always-loaded MCP core at the agreed seven tools.

Findings not changed

• tools/list regression ceiling is 640 KiB (measured ~627 KiB). Bounding the remaining canonical schemas is a separate deletion.
• tracedecay_read still defaults to mode=full.
• Message search still defaults include_subagents to true.

Test plan

• After the tip merge: hooks::steering (2), tools::render::tests (9), catalog always-load and summary-default tests, mcp_suite status_runtime_test (10) and managed_skill_mcp_tools_list_and_view_profile_store (1)
• tracedecay-code-index-runtime compiled as a dependency of those runs after the conflict resolution
• Full workspace cargo nextest not run

Checklist

• CHANGELOG.md updated (release-please owns this file; no Unreleased section)
• No secrets, credentials, or .env files included
• Behavior change: omitted MCP status/skill-view flags are compact. Opt in to the previous raw sections.

  

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[ScriptedAlchemy]

Integrated or superseded directly on the #707 branch at ff36c4f; follow-up compile/typecheck regressions were fixed on that branch.