chore: drop dead code, a fossil manifest comment, and an AGENTS.example.md over its own cap

[Max17190]

Why

An audit of the tree for accidental bloat, run after #222. The repository itself is clean (68 tracked files, all source; 2.4 MiB pack, no binaries or assets ever committed; the release binary is 7.18 MB on Linux against the 8 MB soft gate, up 0.23 MB across the round-4 stacks with open_max_core at 1.2 MiB of a 4.0 MiB .text and no unexpected crate in the breakdown; the frozen prompt measures 5,324 of its 5,360-char cap, 1,218 o200k tokens). Four small things did not belong, and one of them was silently costing every session in this repo.

• AGENTS.example.md overflowed its own cap. agents_md() injects at most 2,000 bytes (MAX_AGENTS_MD_BYTES); the shipped template had grown to 2,854. A verbatim copy was cut mid-sentence at inspect before edit; m followed by the truncation note, so every rule under Development (verify commands, "prefer skill/tool/hook/permission file first, always-on costs tokens", "never invent paths", branch and commit rules, and the closing "Token tax?" question) never reached the model. Confirmed on the wire against a scripted endpoint. Each bullet added to "What ships" pushed the rules at the bottom off the end, and most of those bullets duplicate what the frozen prompt already says on every request (extension paths, --check, --spec, PLAN.md, providers).
• Three #[allow(dead_code)] items in transcript.rs that were dead in fact: BlockKind::Thinking is never constructed (thinking renders as live-tail meta behind ctrl+t, not as a transcript block), and is_following() and scrollbar() have no callers.
• doctor.rs pushed each tool name into external_names and then rebuilt the vector wholesale from tools_found (fix(core): --check counts warned tools as live names for rules and filters #165), with an #[allow(unused_assignments)] hiding the dead push.
• crates/tui/Cargo.toml carried feature notes for syntect (default-syntaxes, default-themes, regex-fancy), a crate that is in neither Cargo.lock nor the source.

Summary

• AGENTS.example.md: 1,930 bytes. Keeps the thesis, the "Not in core / Use instead" table, "Not shipped", the repo map, and every Development rule; the "What ships" list collapses to one paragraph naming what the frozen prompt does not (global ~/.openmax/ mirrors, --approve for hooks and allow rules, --trust-project).
• prompt.rs: agents_example_fits_the_injection_cap measures the file the way agents_md() does and names the fix ("trim it rather than raising the cap"). It fails on the old file (2,854 bytes) and passes on the new one.
• transcript.rs, doctor.rs, crates/tui/Cargo.toml: the removals above. Clippy adjudicated each: zero warnings with the allows gone.
• Deliberately untouched: SandboxPolicy.ro_root (a documented intent field, feat(core): SandboxPolicy in the process spawn path #204), the ignored perf-measurement tests, and the two "use instead" skills.

Test Plan

• Guard red/green: with main's AGENTS.example.md restored the new test fails with AGENTS.example.md is 2854 bytes; agents_md() injects at most 2000; with the trimmed file it passes.
• cargo test --workspace: 810 passed, 0 failed, 8 ignored. cargo clippy --workspace --all-targets: zero warnings.
• Release binary is byte-identical to main (7,042,656 bytes on macOS): the linker was already discarding the dead code, so this is source hygiene, not size.
• Local AGENTS.md copies of the old template are also over the cap; this checkout's was refreshed from the trimmed text (1,953 bytes) and now injects whole.

Greptile Summary

The prompt-template cap guard now fails when a present template cannot be read, while the focused workspace check confirms the tracked template fits the injection limit. The previous broad read-error behavior is no longer present: placing a directory at the expected template path caused the test to exit with an Is a directory error and panic at crates/core/src/prompt.rs:679 instead of returning successfully.

Confidence Score: 5/5

No blocking failure remains.

The non-missing filesystem error path fails the guard as intended, and the focused cap test passes for the tracked template.

T-Rex Logs

What T-Rex did

• Built and extracted a package-equivalent core crate and ran the focused prompt-cap guard without the workspace template; it printed the missing-template skip and passed.
• Reran the guard with a directory at the expected template path; it reported Is a directory (os error 21) and exited with code 101 at src/prompt.rs:679:23.
• Ran cargo test -p open-max-core agents_example_fits_the_injection_cap in the current workspace; the focused cap guard passed.
• Prepared and attached the authored harness and its exact invoked commands to support validation.
• Provided a cross-proof validation summary indicating no regression observed and that the focused workspace run passed with the 2,000-byte injection cap; supporting artifacts are attached.

_{Ran code and verified through T-Rex}

_{Reviews (3): Last reviewed commit: "test: only an absent AGENTS.example.md s..." | Re-trigger Greptile}