code-index: unrepresentable Git paths vanish from the snapshot while status reports complete

[ScriptedAlchemy]

Problem

Code-index capture drops a Git path that no logical path can carry (CapturedFileOutcomeV1::Unrepresentable, e.g. a literal backslash, a control character, or leading/trailing whitespace) from the roster. The only trace is a tracing::warn! (code_index_sources_skipped_unrepresentable_path). No snapshot row, disposition, coverage count or status field records it, so status still reports the index as complete and fresh while a tracked source file is missing. This is the "catch and downgrade to a log line" shape AGENTS.md forbids. It was introduced by #2429 (171aede), whose regression test backslash_paths_are_skipped_and_the_worktree_stays_fresh asserts the vanishing as the intended outcome.

Privacy-withheld files get a snapshot row (Ignored), but the withheld reason is also only logged (code_index_sources_withheld_by_privacy), so the same fix should carry it.

Reproduction (debug CLI from origin/master 9b79b48 plus a configuration-only change, code-index code unchanged; isolated HOME; one daemon under MemoryMax=6G)

$ git ls-files
docs/guide.rs
src/lib.rs
"src/odd\\name.rs"

$ tracedecay tool tracedecay_status --args '{"format":"json","wait_for":{"state":"fresh","timeout_ms":60000}}'
code_index_freshness.worktree: {"coverage": "complete", "staleness_state": "fresh", ...}  wait: {"outcome": "reached"}

$ tracedecay tool tracedecay_files --args '{"format":"json"}'
{"count":1,"files":[{"bytes":17,"path":"src/lib.rs","symbols":1}],"layout":"grouped"}
   (docs/guide.rs is excluded by the configured index.exclude.v1 `docs/**`; src/odd\name.rs is simply gone)

daemon log, the only record:
WARN ...git_tree_capture: code_index_sources_skipped_unrepresentable_path skipped=1 named=src/odd\name.rs

Why it was not fixed in the root-cause-swallowed-errors lane

• The roster (CapturedFileRosterV1::push/finish) is in git_tree_capture.rs. The worktree capture that the fix(code-index): skip Git paths no logical path can carry #2429 test exercises (capture_authoritative_snapshot*) and active-generation reuse are in code_index_scheduler/reconcile.rs, which another root-cause lane owns. Status freshness is projected from the sealed generation in code_index_scheduler/registry.rs (dashboard_freshness_identity), which the layered-generations lane owns.
• A snapshot row needs a logical path that passes validate_code_logical_path, which is exactly what these paths fail. "Reuse the omitted disposition" therefore needs a naming decision first.

Proposed design

1. Domain: add SnapshotFileDispositionV1::Unrepresentable (an omitted disposition, never Present). Name the row with a deterministic, reversible escape of the raw Git path bytes, placed where no tracked Git path can collide. Git refuses .git path components, so a .git/unrepresentable/<hex of raw bytes> style name is collision-free. The alternative, percent-escaping in place, can collide with a real file literally named a%5Cb.rs.
2. Capture: CapturedFileOutcomeV1::Unrepresentable becomes an omitted row through omitted_source_file, like Withheld. Delete unrepresentable_paths and its warn. The freshness witness needs no change: SourceContentManifestV1::for_snapshot keeps only Present rows, and the sweep already filters invalid candidates.
3. Coverage: production/helpers.rs::coverage_summary counts the disposition (for example under files_excluded, or a new typed count). Status adds a typed omitted-sources projection with count and reason (unrepresentable path, privacy withheld) from the sealed snapshot in registry.rs. It must not demote CodeIndexFreshnessCoverageV1 to partial, because is_authoritative() requires Complete and wait_for: fresh would then never be reached for such a repository.
4. Consumers with exhaustive matches: omitted_file_occurrence_id, dashboard code_reads.rs (RevisionPairFileDispositionV1, a contract regen), native_integration/analysis.rs, and search-eval candidate_output.rs.
5. Test (fails on master): a Git fixture with src/odd\name.rs, mounted through CodeIndexSchedulerRegistryV1. Assert that the sealed snapshot holds the row with Unrepresentable, that the status omitted-sources projection reports 1 with that reason, and that the worktree stays fresh on an unchanged probe (the property fix(code-index): skip Git paths no logical path can carry #2429 protects).

Related, same area (code-read only, not runtime-verified)

• capture_exact_git_tree_snapshot names blobs with entry.filepath.to_str_lossy(). Invalid UTF-8 path bytes become U+FFFD, which validate_code_logical_path accepts, so such a file is indexed under a name that does not exist, and two such names in one directory can collide.
• code_index_scheduler/activation.rs: a failed deferred mount is logged with tracing::warn! and the route returns to idle. There is no typed state.

[ScriptedAlchemy]

claimed by fleet slug close-all-issues/code-index-correctness