600-line cap. wc -l AGENTS.md must stay at or under 600, checked as part of every edit — not deferred to a later cleanup.
Offset growth in the same edit. If a change would push the file over the cap, remove or move at least as many lines as you add before finishing the edit. Do not land growth and plan to trim later.
No large table of contents. The "Task-specific guidance" pointer table stays at 12 rows or fewer, holding only the highest-value entries. docs/README.md provides immediate acquisition and curates broader routes, but does not catalog every focused document. Do not grow a second TOC inside AGENTS.md.
Protect the root README boundary. If an AGENTS edit changes documentation entrypoint guidance, preserve README.md as a product landing page of 120 lines or fewer. It features only daily-driver and delightful demo capabilities; every featured capability has a runnable CLI command and a https://dotnet-inspect.net/?w=... packet URL for the same view. Detailed behavior belongs in docs/cli-reference.md, a focused guide, or a product skill.
Protect operator templates. The theme/status reminder, tmux command and state block, round report, and their invocation rules must remain directly in AGENTS.md. Never remove, shorten to a pointer, or move them to meet the line cap; extract another whole section instead.

What belongs in AGENTS.md vs. a doc

AGENTS.md holds binding, cross-cutting rules: things nearly every session needs regardless of which subsystem it touches. Everything else — mechanics, worked examples, tables of edge cases, rationale, historical context — belongs in a focused doc under docs/, docs/design/, docs/runbooks/, or docs/templates/, with a short pointer left in AGENTS.md.

Test before adding prose: would an agent doing unrelated work (say, a decompiler fix) need this fact in the next 30 seconds? If yes, state the rule in one or two sentences and stop there. If the value only shows up once an agent is deep in a specific task, it belongs in that task's owning doc instead.

Workflow for changing AGENTS.md

Run wc -l AGENTS.md to record the baseline before editing.
Write new binding policy as the shortest statement of the rule itself — not its rationale, mechanics, or examples.
Put any accompanying detail (steps, tables, worked cases) in the owning doc and link to it. Prefer creating a new focused doc over inflating an unrelated one or leaving the detail in AGENTS.md.
Confirm the protected theme/status, tmux, and round-report templates and their invocation rules are still present verbatim enough to use without opening another file.
Re-run wc -l AGENTS.md. If still over 600, migrate another whole section or subsection to its owning doc — see the extraction checklist below. Repeat with a full section each time; do not switch to shaving individual lines to close a small remaining gap.
When documentation entrypoint guidance changed, run wc -l README.md and confirm the landing-page boundary above still holds.
Run npx markdownlint-cli AGENTS.md (and any doc you edited) before committing.

Extraction checklist when over budget

Move content in whole, section-sized blocks, not by trimming prose word by word. A block move is legible as a genuine reorganization; shaving a line here and there to squeak under the cap is not — it reads as gaming the number and tends to fuse unrelated sentences, drop headings that readers or other docs depend on, or otherwise degrade the file it was supposed to keep skimmable.

A whole subsection whose detail belongs in a focused doc: cut the entire subsection over, leave one summary paragraph plus a pointer in AGENTS.md.
A bullet that restates a longer explanation already in the linked doc: keep the bullet, delete the restatement.
A rarely invoked scenario (well under one PR in twenty): reduce to a single pointer sentence, as with the Markout co-development loop.
The protected operator templates are never extraction candidates. If they create pressure, move a different whole subsection.

If after moving the obvious block-sized candidates the file is still over (or barely under) 600, that is a signal to find one more whole section to relocate — not to start merging headings into prose, deleting blank lines between unrelated paragraphs, or rewording sentences purely to save a line. Never remove or fold a heading to save space; if it is not clearly disposable as a whole subsection, leave it and find a different block to move instead.

Table of contents discipline

Keep the "Task-specific guidance" table at 12 rows or fewer. Choose entries by how often an agent needs them, not by comprehensiveness.
When a new entry would push the table past 12, swap out a lower-value row. Add a docs/README.md route only when the destination is itself a high-value entrypoint; otherwise rely on focused owner and consumer links.
Update docs/README.md only when its acquisition block, a curated route, or an entrypoint role changes.

Validation

wc -l AGENTS.md   # must be <= 600
wc -l README.md   # must be <= 120
npx markdownlint-cli AGENTS.md

update-agents-md

Updating AGENTS.md

Hard constraints