Add targeted instruction source replacement

[andrei-hasna]

Summary

• add fail-closed source:<normalized-source-id> replacement that removes exactly one earlier overridable source
• preserve unscoped broad replacement while recording the targeted relation in manifest provenance and skipped-source output
• add CLI --replace-source replacer=target parity with identity-exported replacementScope

Validation

• bun test src/lib/session-render-silent-source-drop.test.ts src/cli/session.test.ts — 32 pass, 0 fail
• bun test — 660 pass, 0 fail
• bun run typecheck
• bun run build
• repository package-manager scan — clean
• staged and committed-patch secret scans — zero findings

Candidate

• base: 8b785d6a09b8bb4abd48c7538cdf32418320d5e0
• head: fafec2a88522ad6bda43dcba3af4618b878df584

Rollback

• git revert fafec2a88522ad6bda43dcba3af4618b878df584

[andrei-hasna]

[REVIEW] GO — #80 @ fafec2a — lens: correctness+security+gates, reviewer Timon (1 of 1)

Exact candidate reviewed

• Base: origin/main at 8b785d6.
• Head: fafec2a.
• Read: full diffs and surrounding source for src/cli/index.tsx, src/cli/session.test.ts, src/lib/session-render.ts, and src/lib/session-render-silent-source-drop.test.ts. I also traced CLI source collection, identity-export normalization, semantic-policy deduplication, ordered composition, manifest/provenance generation, and broad-replacement compatibility.

Commands and results

• git log --oneline origin/main..HEAD — exit 0; one commit, fafec2a.
• git diff origin/main...HEAD --stat — exit 0; 4 changed files, 695 insertions, 17 deletions.
• bun install — exit 0; setup only, 158 packages installed.
• bun run typecheck — exit 0; tsc --noEmit, no diagnostics (the gate does not emit pass/fail counts).
• bun run test — exit 0; 660 pass, 0 fail, 2765 expect() calls across 56 files.

Blocking P0/P1 findings

• None.

Security and correctness assessment

• Targeted replacement is bounded to one normalized, earlier, overridable source and fails closed for missing, later, ambiguous, already-removed, malformed-scope, append-mode, non-overridable, and semantic-deduplication cases.
• The rendered manifest records the replacement scope, skipped target, and replacer provenance; the source hash changes with the replacement relation.
• Existing unscoped broad replacement behavior remains covered and green.
• The change does not add a new credential, filesystem-write, command-execution, or authorization sink.

Non-blocking follow-ups

• None.