perf(prompt): compact the skills guidance preamble, -218 always-on tokens (salvage #72813) [needs wording sign-off]

[kshitijk4poor]

Context

The skills-guidance preamble (the prose block above <available_skills> instructing the model when/how to load skills) is paid on EVERY session's system prompt, for every user with skills installed — and it had grown to 1,550 chars of overlapping instructions. This compacts it to 678 chars while preserving every behavioral contract the long form carried.

Measured impact

387 → 169 tokens (−218 tokens, −56%) of always-on system-prompt weight for any session with skills, measured on a live build_skills_system_prompt render.

The wording gate (flagging for maintainer sign-off)

This is a REWORDING of tuned behavioral prompt copy, so it can shift model behavior — that's a taste/behavior call, not a mechanical merge. Mitigation shipped with the PR: a disclosure-contract test asserts the compacted string still carries each key behavioral phrase (MUST-load on match, partial-relevance loading, hermes-agent-skill-first rule, patch-when-stale, offer-to-save-after-hard-tasks). If maintainers want the long form back for any single behavior, the test names exactly which phrase anchors it. Requesting explicit sign-off on the wording rather than silent auto-merge — NOT arming auto-merge on this one.

Provenance

Salvage of #72813 by @JeremyDev87 (authorship preserved; attribution mapping merged as #77685). The PR's delegate_tool.py hunks were dropped as superseded — main already rewrote _build_top_level_description to the static duplication-free design this PR was reaching for; what survives is the prompt_builder compaction.

Verification

• tests/agent/test_prompt_builder.py 56 passed / 1 skipped.
• Mutation check: reverting prompt_builder.py fails the new disclosure-contract test; restore green.
• Zero skills hidden: the <available_skills> entries are byte-identical before/after (only the preamble prose changed).

Closes #72813.

[Ruanjq98]

Code Review: #77698

Verdict: Approve

Test: additional coverage.

LGTM - Reviewed diff. Changes are sound.

[GottZ]

This was generated by AI during triage.

Summary

Two PRs address Issue #72737. #72813 compacted both the skills preamble and delegation guidance, while #77698 preserves only the skills-preamble compaction because the delegation portion was superseded by #77372.

Related pull requests

• perf(prompt): compact skill and delegation guidance #72813 [closed] best fix — (+147/-82) — n/a: Compacts both always-on prompt surfaces and adds contract tests; it remains relevant as the recorded best-fix and source implementation, but is closed because its skills portion was salvaged as perf(prompt): compact the skills guidance preamble, -218 always-on tokens (salvage #72813) [needs wording sign-off] #77698 and its delegation portion was superseded by perf(tools): compact delegate_task description by deduping against param schema #77372. Despite the earlier keep_open review, later contributor comments explicitly document both replacement paths and confirm that perf(prompt): compact the skills guidance preamble, -218 always-on tokens (salvage #72813) [needs wording sign-off] #77698 retains the iterative-task trigger and cronjob restriction concerns raised by that review where applicable.
• perf(prompt): compact the skills guidance preamble, -218 always-on tokens (salvage #72813) [needs wording sign-off] #77698 related — (+44/-20) — n/a: Salvages perf(prompt): compact skill and delegation guidance #72813's skills-preamble diff, retaining partial-relevance and uncertainty loading, Hermes-first guidance, stale-skill patching, the difficult/iterative save trigger, and a compactness/contract test; it intentionally omits the superseded delegation changes. The non-contributor review approves the diff, while the author requests maintainer wording sign-off because prompt copy affects behavior.

Duplicates

#72813 and #77698 contain essentially the same skills-preamble compaction and test; #77698 is the focused salvage, while #72813's additional delegation work is not duplicated there and was superseded by #77372.

Suggested consolidation

Keep #77698 open with a salvage path: obtain the requested maintainer wording sign-off on its focused skills-preamble compaction and contract test. #72813 is already closed in favor of #77698 for that portion, with its delegation portion superseded by #77372, so no reopen or additional duplicate closure is needed.

Cross-PR triage: Reviewed 2 pull requests and 1 issue in this complex. Each diff was read against this issue; Assessment working set: 21 kB of PR diffs, 8 kB of issue/PR text, 1 kB of discussion (3 comments), 3 verify verdicts. verdicts reflect diff content, not PR titles. Part of an automated triage batch.