refactor(coding-agent): move the semantic-edge ledger onto the event-log substrate

[snimu]

Purpose

The ACP semantic-edge ledger (#1885) and the RLM spawn ledger implement the same append-only JSONL crash-safety independently. #1987 extracted that mechanics into event-log.ts and moved the spawn ledger onto it; this PR completes the dedup by moving the semantic-edge ledger's private append/replay/repair IO onto the same substrate. EventLog is now the single owner of torn-tail handling, repair-on-append, and line-level replay for both ledgers.

What changed

• SemanticEdgeRecorder keeps its semantics (degrade-to-disabled on the first ledger failure, write-before-action ordering, replay-on-resume, retry-identity parking) and deletes its IO: _loadExisting, parseLedgerContent, _pendingRepair (truncate/terminate memo), and the mkdir/appendFileSync plumbing are gone; construction replays through EventLog and appends go through EventLog.appendSync
• readSemanticEdgeLedger keeps its contract: reads never mutate or create the file, a missing ledger throws (statSync probe), interior corruption stays loud with the same corrupt semantic-edge ledger line N message

One durability rule unified (union, not intersection)

The two IO layers disagreed on a parseable-but-unterminated final line: the edges ledger newline-completed it (keeping the record), the substrate truncates it (#1987's review verdict: completion turns a line a strict parser rejects into permanent fail-closed interior poison). Worse, the substrate's replay still surfaced such a line while its next append destroyed it — reading data the log then disowns. This PR unifies on one coherent rule in the substrate, for both ledgers: an unterminated final line is an uncommitted append — skipped on read (with the torn-final-line log) and truncated before the next append. This state is unreachable from either ledger's own single-write appends (record and newline are one write); it matters only for crash/interference windows, where "uncommitted" is the only safe reading.

Test surface

• rlm-ledger.test.ts: passes unchanged
• semantic-edges.test.ts: one test edited — the pin of the old newline-completion behavior now pins the unified truncation semantics (skipped on read, truncated on append); flagged for exactly this migration in the refactor(coding-agent): extract the append-only event-log substrate from the RLM spawn ledger #1987 review. Everything else (torn-tail tolerance, repair-once, read-never-mutates, read-never-creates, corruption messages, disable-on-failure) passes unchanged
• event-log.test.ts: the JSON-parseable-tail pin gains the read-side assertion; both behavior pins verified fail-unfixed against the pre-change substrate

Validation

• sanitized suites: event-log, rlm-ledger (unchanged), semantic-edges (52), agent-session-semantic-edges (23, incl. the fix(coding-agent): settle late compaction slices and forward daemon subagent lineage #2021 settle-race pin), agent-traces (45, incl. the feat(coding-agent): deliver the semantic-edge ledger through the agent-traces outbox #1984 consent-gated intent and outbox pins), suite/agent-session-compaction — 187 tests, 0 failures
• root npm run check (biome, tsgo, installer render, browser smoke) passes via the pre-commit hook

LOC

Total src: +59/−117 (net -58); tests: +79/−5 (net +74).
Tests +11/−4, changelog +1. Classification: deletion — duplicated IO mechanics removed; the only mechanism change is the read-side half of the unified unterminated-tail rule, which removes an inconsistency rather than adding a branch.

Linear: RES-1260 https://linear.app/primeintellect/issue/RES-1260

---

Note

Medium Risk
Changes durable ledger I/O and tail semantics for semantic-edge sessions (parseable torn tails are dropped on resume), though normal single-write appends are unaffected; repair failures now block appends instead of being swallowed.

Overview
Routes ACP semantic-edge ledger append/replay through shared EventLog, removing bespoke _loadExisting, parseLedgerContent, and deferred truncate/newline repair in SemanticEdgeRecorder. readSemanticEdgeLedger replays via EventLog with missingFileThrows so a missing file still errors for explicit readers.

EventLog tightens crash semantics for both ledgers: unterminated final lines are always treated as uncommitted (skipped on replay even when JSON-valid, truncated on next append—never newline-completed). appendSync fails on short writes instead of silently partial appends; repairTailSync surfaces repair failures so appends do not write through an unrepaired torn tail.

Tests add fault-injection coverage for short writes and failed truncation; semantic-edge expectations shift from newline-completion to the unified tail rule.

^{Reviewed by Cursor Bugbot for commit d749cf9. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Move semantic-edge ledger onto EventLog substrate

• Replaces the recorder-local file I/O in semantic-edges.ts with shared EventLog.replaySync and EventLog.appendSync calls in event-log.ts, consolidating tail repair, write verification, and missing-file handling into EventLog.
• EventLog.replaySync now skips any unterminated final line (even valid JSON) and can optionally throw on a missing file.
• EventLog.appendSync writes via a UTF-8 buffer and throws on short writes instead of silently treating the partial append as complete.
• EventLog.repairTailSync propagates open/read/truncate errors instead of swallowing them, and truncates a stable unterminated tail at the last newline.
• Adds fault-injection tests in event-log-faults.test.ts covering short writes and unrepairable tails, and updates existing semantic-edge and event-log tests for the new tail-skip behavior.
• Risk: EventLog.replaySync no longer surfaces parser errors from an unterminated final line; callers that relied on such errors will see that line skipped instead.

^{Macroscope summarized d749cf9.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit e88fc98. Configure here.}