fix(composer): require corroboration before empty-classifying left-bar idle hints

[pablontiv]

Intent

Captain's intent: dispatch now. Fix GitHub issue #4477 in this fork and open a PR through the normal contribution flow, with exact issue linkage (the PR must close #4477). This is a reproduced dangerous-direction false-empty defect in a distinct composer path from the recently-shipped bordered-box hardening (#2483/PR #4452).

Issue #4477 substance: _fm_composer_classify_leftbar (bin/fm-composer-lib.sh:1104) skips a row as furniture using an unanchored/prefix match against FM_COMPOSER_IDLE_RE/FM_COMPOSER_IDLE_RE_DEFAULT, gated only by placeholder_position (the first non-blank content row after a leading blank left-bar row), with NO independent-empty corroboration - pending_seen=0 unconditionally yields empty. A real, genuinely-unsent draft that begins with a placeholder phrase (e.g. the default Ask anything...) is misclassified empty instead of pending. Confirmed live using the OpenCode 1.18.30 capture shape already in tests/fm-composer-lib.test.sh:411: Ask anything... please reply at placeholder_position=1 -> wrongly empty; Reply with OK. at the same shape -> correctly pending. This path (OpenCode/Grok/Kimi's left-bar composer) is MORE exposed than the bordered-box path because it has no empty_seen-style corroboration gate at all - a single swallowed row is sufficient to misclassify. The sibling bordered-box hardening requires an exact full-row furniture match rather than a prefix or substring and requires at least one independent row to prove empty before returning empty.

What Changed

• _fm_composer_classify_leftbar (bin/fm-composer-lib.sh) no longer treats a placeholder-position idle-hint match alone as proof of an empty composer: it now tracks empty_seen, set only by an independently blank/ghost-stripped row, and returns unknown instead of empty when no such corroboration exists.
• FM_COMPOSER_IDLE_RE_DEFAULT is tightened so the Ask anything... idle pattern only matches an optional single trailing quoted suggestion (([[:space:]]+"[^"]*")?$) instead of an unanchored prefix, so a real draft that starts with the placeholder phrase (e.g. Ask anything... please reply) is no longer swallowed as furniture; both _fm_composer_classify_leftbar and fm_composer_extract_selected_content build and use this anchored furniture_re instead of matching the raw idle regex.
• Adds coverage in tests/fm-composer-lib.test.sh for a placeholder-prefixed draft (classified pending), a furniture-only left-bar row with no corroborating blank (classified unknown), and selected-content extraction preserving placeholder-prefixed input.

Risk Assessment

✅ Low: The fix directly addresses the issue's root cause (unanchored idle-placeholder regex + missing independent-empty corroboration in the leftbar path), mirrors the sibling bordered-box hardening as required, is covered by new tests that reproduce the exact reported failure and pass/fail appropriately, and I traced the row-loop logic against both new and pre-existing test screens without finding a silent misclassification.

Testing

Ran the actual bash composer-classifier library through its existing test suite at the target commit (all pass, including two new regression assertions for the exact issue-#4477 shape), then live-reproduced the reported defect by temporarily substituting the pre-fix library file and observing the same test fail exactly as described, confirming this is a genuine fix; worktree was restored clean afterward.

• Live validation: ✅ go - 5 of 6 scenarios driven live against the product

Scenario	Result	Live	Evidence
Placeholder-prefixed real draft is no longer swallowed as empty	✅ pass	live	bash tests/fm-composer-lib.test.sh at target commit dd91570: ok - matrix: opencode's left-bar composer reads empty everywhere and scans the full active run (includes the 'opencode 1.18.30 placeho…
Regression reproduction: same scenario misclassified as empty on pre-fix code	✅ pass	live	Swapped bin/fm-composer-lib.sh to the base commit (a6618dd) version in place while keeping the fixed test file, reran suite: `not ok - opencode 1.18.30 placeholder-prefixed draft on tmux: expected pe…
Furniture-only single row (no corroboration) now reads unknown, not empty	✅ pass	live	Same test function assertion 'opencode furniture-only left-bar lacks empty proof' expects unknown; part of the passing ok - matrix: opencode's left-bar composer... line in the target-commit run.
Genuine idle placeholder (uncorroborated-but-blank-backed) still reads empty; genuine typed text still reads pending	✅ pass	live	Pre-existing assertions in the same test function ('opencode idle on tmux', 'opencode 1.18.30 completed-turn idle hint on tmux', 'opencode 1.18.30 completed-turn typed composer on tmux') all passed in…
Selected-content extraction preserves placeholder-prefixed user text instead of dropping it as furniture	✅ pass	live	ok - fm_composer_extract_selected_content: scopes user content and excludes furniture in target-commit run includes the new assertion that 'Ask anything... please reply' extracts verbatim rather tha…
PR opened with exact 'Closes #4477' linkage	⏸️ untested	no	Out of scope for this test phase per the gate-step phase boundary: PR creation/push is owned exclusively by the outer executor's other phase(s), not by this assigned test phase.

Pipeline

Updates from git push no-mistakes

✅ **intent** - passed

✅ No issues found.

✅ **Rebase** - passed

✅ No issues found.

⚠️ **Review** - 1 info

• ℹ️ bin/fm-composer-lib.sh:1077 - furniture_re="^(${idle_re})$" is built identically in two places (_fm_composer_classify_leftbar and fm_composer_extract_selected_content). Could be a shared one-line helper, purely mechanical dedup.

✅ **Test** - passed

✅ No issues found.

• Live validation: ✅ go - 5 of 6 scenarios driven live against the product

Scenario	Result	Live	Evidence
Placeholder-prefixed real draft is no longer swallowed as empty	✅ pass	live	bash tests/fm-composer-lib.test.sh at target commit dd91570: ok - matrix: opencode's left-bar composer reads empty everywhere and scans the full active run (includes the 'opencode 1.18.30 placeho…
Regression reproduction: same scenario misclassified as empty on pre-fix code	✅ pass	live	Swapped bin/fm-composer-lib.sh to the base commit (a6618dd) version in place while keeping the fixed test file, reran suite: `not ok - opencode 1.18.30 placeholder-prefixed draft on tmux: expected pe…
Furniture-only single row (no corroboration) now reads unknown, not empty	✅ pass	live	Same test function assertion 'opencode furniture-only left-bar lacks empty proof' expects unknown; part of the passing ok - matrix: opencode's left-bar composer... line in the target-commit run.
Genuine idle placeholder (uncorroborated-but-blank-backed) still reads empty; genuine typed text still reads pending	✅ pass	live	Pre-existing assertions in the same test function ('opencode idle on tmux', 'opencode 1.18.30 completed-turn idle hint on tmux', 'opencode 1.18.30 completed-turn typed composer on tmux') all passed in…
Selected-content extraction preserves placeholder-prefixed user text instead of dropping it as furniture	✅ pass	live	ok - fm_composer_extract_selected_content: scopes user content and excludes furniture in target-commit run includes the new assertion that 'Ask anything... please reply' extracts verbatim rather tha…
PR opened with exact 'Closes #4477' linkage	⏸️ untested	no	Out of scope for this test phase per the gate-step phase boundary: PR creation/push is owned exclusively by the outer executor's other phase(s), not by this assigned test phase.

• bash tests/fm-composer-lib.test.sh (target commit dd915706, bin/fm-composer-lib.sh as shipped) — 34/34 ok, exit 0
• bash tests/fm-composer-lib.test.sh (base commit a6618ddc bin/fm-composer-lib.sh swapped in, fixed test file retained) — reproduces the reported defect: 'expected pending, got empty' for the placeholder-prefixed draft, exit 1
• bash tests/fm-composer-lib.test.sh (restored target file) — re-verified clean pass, worktree confirmed clean via git status --short

✅ **Document** - passed

✅ No issues found.

✅ **Lint** - passed

✅ No issues found.

✅ **Push** - passed

✅ No issues found.