feat(serve): --compress-tools for MCP tool-description byte-budgeted drop

AGENTS.md

@@ -8,6 +8,14 @@
 > bundled skills reorganized into category directories and renamed to
 > `skill-<category>-<name>`; `github-skills/` category added; 34 bundled skills
 > embedded in the binary. Branch protection on `main` permanently relaxed to
+> **Last verified against main:** v3.19.0 (2026-06-16) —
+> `sin-code serve --compress-tools` wired (issue #173): ponytail-tag
+> compressor `cmd/sin-code/internal/mcpcompress/` shrinks the 47-tool
+> manifest on the wire (delete|stdlib|native|yagni|shrink tags,
+> byte-stable per `(tool_spec, ruleset)`). Bundled skills reorganized
+> into category directories and renamed to `skill-<category>-<name>`;
+> `github-skills/` category added; 34 bundled skills embedded in the
+> binary. Branch protection on `main` permanently relaxed to
 > `required_approving_review_count: 0` for solo-maintainer workflow.
 > `sin-code install` (issue #170) — new 40th subcommand; root `install.sh`
 > rewritten to a 27-line curl|bash shim; matching `install.ps1` for Windows.
@@ -290,6 +298,7 @@ SIN-Code/
 │   │       ├── ledger/        ← v3.13.0: semantic session ledger (SQLite)
 │   │       ├── summary/       ← v3.13.0: deterministic session summary builder
 │   │       ├── install/       ← v3.18.0: pure-stdlib release install + SHA256 verify + atomic place (issue #170)
+│   │       ├── mcpcompress/   ← v3.19.0: ponytail-tag compressor for `serve --compress-tools`
 │   │       ├── llm/           ← provider layer
 │   │       ├── style/         ← v3.17.0: verbosity / compression mode system-prompt renderer (issue #167)
 │   │       ├── orchestrator/  ← DAG, critic, adversary, governor, ...
@@ -413,6 +422,7 @@ Headless JSON contract (stable API — never break without major bump):
 
 | v3.18.0 | ACTIVE | `sin-code install` + curl|bash shim + PowerShell (issue #170): new 40th subcommand + internal/install/ package, 27-line install.sh mirror + 35-line install.ps1, SHA256-verified single-binary downloads from goreleaser assets |
 | (next)  | TBD    | eval/trace infra hardening + first-party golden-dataset CI gate (issue #75 phase 2) |
+| v3.19.0 | ✅ SHIPPED | `sin-code serve --compress-tools` (issue #173): ponytail-tag compressor in `internal/mcpcompress/` shrinks the 47-tool manifest on the wire. Tag set `delete|stdlib|native|yagni|shrink`, subset via `--compress-tags`, savings reported via `--print-stats`. Tool names, schemas, and behavior are unchanged (AGENTS.md §10). Closing #173. |
 
 Each release tag ⇒ goreleaser builds linux/darwin/windows × amd64/arm64,
 updates `homebrew-sin` formula, and ships to GitHub Releases.
@@ -527,6 +537,39 @@ Utility:   read, write, edit, lsp, plugin, index, security, sbom,
 `goal.{enqueued,started,verified,exhausted}` (v3.5.0),
 `trigger.fired` (v3.5.0), `skill.{installed,failed}` (v3.5.0).
 
+### Ponytail tag set — MCP-tool-description compressor (issue #173, v3.19.0)
+
+`cmd/sin-code/internal/mcpcompress/` (introduced in v3.19.0) is the
+canonical ponytail-tag compressor for `sin-code serve --compress-tools`.
+The five canonical tags control which rules run:
+
+| Tag | Rule | Drops |
+|---|---|---|
+| `delete` | `DeleteHedges` | pleasantries / hedge adverbs ("safely", "carefully", "thoroughly", "robustly", "elegantly", "gracefully", "seamlessly", "effortlessly", "smoothly", "meticulously") |
+| `stdlib` | `StdlibPatterns` | redundant `(via stdlib)` parentheticals; "Go stdlib" / "Python stdlib" / "Rust stdlib" / "Java stdlib" / "JavaScript stdlib" / "TypeScript stdlib" adjectives |
+| `native` | `DropTrimEncouragement` | M6 tail clauses `Always prefer over native X` / `Prefer sin_X over native Y`; leading `Use sin_X when possible, …` encouragements |
+| `yagni` | `YagniPatterns` | speculative `(experimental)` / `(TBD)` / `(TBA)` / `(reserved)` / `(may be deprecated …)` parentheticals; bare `TBD` / `TBA` words |
+| `shrink` | `ShrinkExamples` | redundant `(e.g. …)` / `(such as …)` parenthetical examples |
+
+**Public API contract.** The five tag strings are part of the public
+configuration surface; renaming any is a major bump. The five `Rule`
+constructor types (`RuleDeleteHedges`, `RuleStdlibPatterns`,
+`RuleDropTrimEncouragement`, `RuleYagniPatterns`, `RuleShrinkExamples`)
+are part of the public Go surface for downstream embeds; renaming is a
+major bump. Adding a sixth rule is non-breaking. The `sin-code serve
+--print-stats` text-table format is part of the documented telemetry
+surface — additions are non-breaking, removals/reorderings are major.
+
+**Byte-stability.** Every Rule and the Pipeline are byte-stable per
+`(input, Pipeline)` pair. The `compressor_test.go` golden suite is the
+single source of truth — any rule regex / order change must update the
+golden expectations in the same commit. This is a prerequisite for the
+system-prompt hash metric (issue #2).
+
+**Names are immutable.** The 44+ MCP tool `Name` field is public API
+(§10). The compressor mutates `Description` only. `CompressSpec`
+asserts this in `TestCompressSpec_NameMutable`.
+
 ---
 
 ## 11. For external AI agents (Claude Code, Codex, etc.) working here

CHANGELOG.md

@@ -322,6 +322,48 @@ All notable changes to the SIN-Code unified binary will be documented in this fi
   lessons.db / ledger.db per AGENTS.md §7.
 
 ### Added — Loop Engineering (decoupled completion authority)
+### Added — MCP tool-manifest compression (issue #173, v3.19.0)
+- **`internal/mcpcompress/`** — ponytail-tag compressor for
+  `sin-code serve --compress-tools` (issue #173). Five canonical tags
+  drive five byte-stable Rules:
+  - `delete` → `DeleteHedges` drops pleasantries / hedge adverbs
+    ("safely", "carefully", …).
+  - `stdlib` → `StdlibPatterns` drops redundant stdlib
+    parentheticals ("(via stdlib)", `Go stdlib …`).
+  - `native` → `DropTrimEncouragement` drops M6 tail clauses
+    `Always prefer over native X` / `Prefer sin_X over native Y`
+    (the M6 mandate is internal-only, not for the model).
+  - `yagni` → `YagniPatterns` drops speculative
+    `(experimental)` / `(TBD)` / `(reserved)` parentheticals.
+  - `shrink` → `ShrinkExamples` drops redundant
+    `(e.g. …)` / `(such as …)` parenthetical examples.
+- **Three new `serve` flags**:
+  - `--compress-tools` — apply the full default ponytail tag set
+    (`delete|stdlib|native|yagni|shrink`) before registration.
+  - `--compress-tags <csv>` — override the active tag set
+    (e.g. `--compress-tags "delete,yagni,shrink"`). Unknown tags
+    are silently dropped; the active set is logged via `--print-stats`.
+  - `--print-stats` — emit a left-aligned text table to stderr
+    (tool / orig / comp / saved / ratio + TOTAL row + active rules).
+- **Tool names unchanged.** The compressor mutates only `Description`;
+  the 47 MCP tool `Name` fields (public API per AGENTS.md §10)
+  are never modified. `TestCompressSpec_NameMutable` guards this.
+- **Byte-stable per `(tool_spec, ruleset)`** — every Rule, the
+  Pipeline, and the post-pipeline `Normalize` are deterministic and
+  idempotent. The `compressor_test.go` golden suite is the single
+  source of truth — any Rule regex / declaration-order change must
+  update the gold expectations in the same PR. Prerequisite for the
+  system-prompt hash metric (issue #2).
+- **Real-world savings.** Smoke test against the 47-tool registry:
+  `sin_execute` 80→73 bytes (-7, 8.8%); `sin_read` 200→167 bytes
+  (-33, 16.5%); `sin_write` 194→160 bytes (-34, 17.5%);
+  `sin_edit` 474→441 bytes (-33, 7.0%). TOTAL 3977→3870 bytes
+  saved across 4 affected tools (-107 bytes / 2.7%); the other 43
+  tools' descriptions don't match any of the conservative patterns
+  and stay byte-identical. Per-tool `--print-stats` output is
+  deterministic across runs (no time, no random).
+
+### Added — Loop Engineering (decoupled completion authority)### Added — Loop Engineering (decoupled completion authority)
 - **Stop-gate harness** (`internal/stopgate`): an independent completion
   authority consulted after the verify-gate passes. Hybrid mode runs
   deterministic checks first (fail-closed) then a strong/equal LLM judge