finding(gate): check-shell-escape-residue's content/docs row has no coverage tree, so narrowing or deleting it is still silent — the one root #7413 deliberately left unruled #8011

Filed out-of-scope from #7413 (PR #8010). Unassigned. Zero occurrences today — this is an asymmetry left behind by a deliberate scope decision, not a live defect.

What

#7413 added COVERAGE_TREES to scripts/check-shell-escape-residue.mjs: trees in which every .md/.mdx must be reached by some SCAN_ROOTS row, red by file name otherwise. Two trees were declared:

export const COVERAGE_TREES = Object.freeze([
  { spec: '.claude', kind: 'dir' },
  { spec: 'skills', kind: 'dir' },
]);

content/docs was deliberately not declared, and the gate's docblock says so and why:

⛔ content/docs is deliberately NOT a coverage tree. Same mechanics, but a different claim: this gate's roots are the agent-facing surface (objectui#5151 ruled it, objectui#7403 widened it), and content/docs is published prose that happens to share the scan. Declaring coverage over it would assert a completeness promise about the docs tree that no card has ruled.

The asymmetry that remains

The skills coverage tree was included even though it is a tautology today (its row is the whole tree, 16 of 16), because a tautology is exactly what it stops being under the one edit nothing else catches: narrowing the row to a subtree, or deleting the row. Neither shows up as unresolved — a root that vanishes from disk is loud, a row someone removes from the declaration list leaves nothing behind to be loud about — and both walk a whole tree off the scan surface silently.

content/docs carries that exposure identically and now has no guard against it. Measured on e1545cf: 184 files, 1064 fenced blocks, i.e. 81% of this gate's entire fence population sits behind a row whose deletion is unobservable. The other four roots would keep resolving, every remaining minFiles floor would be met, and FENCE_FLOOR at 400 is cleared by skills alone (210) plus AGENTS.md (15) only in combination — so it is worth measuring rather than assuming: 1309 - 1064 = 245, which is under the 400 floor. So today FENCE_FLOOR happens to catch this one case, by 155 fences, as a side effect and not by design.

That accident is the interesting part. FENCE_FLOOR is documented as a collapse detector for a broken fence walker, explicitly not a coverage floor:

the floor is set far under that on purpose -- it catches a fence walker that stopped matching, not a day when the docs got shorter.

So the protection is incidental, undocumented, and disappears the moment either tree grows: once skills plus AGENTS.md plus .claude/skills exceed 400 fences on their own, deleting the content/docs row becomes fully silent. It is one root away from being the same class as #7403 and #7413.

The decision to make

Not mechanical — it is the same choice #7413 framed and declined to make unilaterally:

1. Declare content/docs a coverage tree. One row; green by construction today (its row is the whole tree, exactly like skills). Cost: the gate then asserts a completeness claim over published docs, which is a promise about a surface no card has ruled it should make.
2. Leave it, and record the incidental FENCE_FLOOR protection in the gate's docblock along with the arithmetic above, so the next person to raise a floor or move a tree can see what they would be spending.
3. Rule that row deletion should be caught generally rather than tree by tree — e.g. pin the SCAN_ROOTS spec list in the test, which catches deletion of any row including this one, at the cost of an edit to the pin whenever the surface legitimately moves.

Option 3 is arguably the general form of the general form, and would make the skills coverage tree redundant. Worth ruling once rather than per root.

Not a duplicate of

• [finding] check-shell-escape-residue's new .claude/skills root does not reach the rest of the agent tree — a future .claude/agents/*.md repeats #7403 exactly #7413 — added the mechanism and named this exclusion; this card is the exclusion itself.
• check-shell-escape-residue lost the same two guides #7251 moved — its skills root does not reach .claude/skills #7403 — the move that created the whole class, .claude/skills.
• 没有任何门禁校验文档里 fenced shell 示例的可执行性:实测 shell 转义泄漏进代码块对全部门禁不可见 #5151 — the card the gate was built on; it ruled the original four roots.

Measured by the dev seat on #7413 while writing the exclusion into the docblock, unclaimed.