feat(install): P4a recoverable handoff reservation and writer floor 2

[777genius]

Stacked on #177 (feat/agent-notify-e2e @ 89d8524). This is P4a only from the UAP installer SDK + notification wizard plan: kernel reservation/intent/floor guard. Default installer routing is unchanged. Do not merge this into #177; keep it as a child PR.

What landed

• Kernel PendingMutation reservation published in the same recoverable transaction as host-owned portable-handoff.json.
• Reservation is required before retiring owned direct MCP/skill; unmatched writers get ErrReservationConflict.
• Transaction schema 3 + writer floor 2 for reservation start/change/cleanup/reverse. Ordinary installs stay schema 2 / floor 1 / managed-writer protocol v1.
• Floor and schema 3 are never lowered on cleanup or rollback.
• Frozen v1 decoder/floor checks reject schema 3 journals and floor 2 ledgers.
• Coordinator process lease (.setup-coordinator.lock) serializes confirmed handoff/resume. Death releases the lease; the persisted reservation remains.
• Recovery-only Recover() / Commit(RecoverOnly) replays a pending journal and returns without refresh, install, or a new consumer.
• Policy-only disable still works on an intact reserved ledger; an open kernel journal still returns ErrPolicyRecovery.
• Kernel does not import portablesetup or UAP types and does not parse intent JSON.
• No-op handoff does not create intent and does not raise the writer floor.
• Current portable locator and setup qualification accept floor 2 so a completed handoff can still launch.

Tests (no Claude/Codex login)

go test ./internal/installruntime/ ./internal/agentnotify/portablesetup/ ./internal/agentnotify/clientsetup/ ./internal/agentnotify/portable/ ./internal/agentnotify/setup/ -count=1

TestRecoverOnlyReplaysJournalWithoutConsumer compares recovered RuntimeRoot through CanonicalPath. TestAgentNotifyProcessBlockedMCP/signal treats SIGTERM as a successful join, using a positive join predicate that satisfies staticcheck QF1001.

Not in this PR (later plan checkpoints)

• P1–P3, P5: public UAP installer API in the UAP repo.
• P4: Notifications portable adapter pin onto that API.
• P6: setup-notifications wizard.
• R3: cross-platform native client E2E.

Plan acceptance for P4a

Reservation blocks conflicting replace/register; intent+reservation are published atomically through the existing transaction; schema 3 + floor 2; old writer rejects pending start/cleanup/reverse; floor is not lowered; coordinator lease; recovery-only kernel entry; no second journal engine.

  

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[codecov]

Codecov Report

❌ Patch coverage is 60.60606% with 130 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.18%. Comparing base (89d8524) to head (e29dbd1).

Files with missing lines	Patch %	Lines
internal/agentnotify/portablesetup/setup.go	60.38%	34 Missing and 27 partials ⚠️
internal/agentnotify/portablesetup/uap.go	17.07%	29 Missing and 5 partials ⚠️
internal/installruntime/reservation.go	74.69%	12 Missing and 9 partials ⚠️
internal/agentnotify/portablesetup/intent.go	62.50%	3 Missing and 3 partials ⚠️
internal/installruntime/recovery.go	66.66%	2 Missing and 2 partials ⚠️
internal/installruntime/transaction.go	84.21%	1 Missing and 2 partials ⚠️
internal/agentnotify/setup/setup.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##           feat/agent-notify-e2e     #180      +/-   ##
=========================================================
- Coverage                  65.27%   65.18%   -0.09%     
=========================================================
  Files                        168      170       +2     
  Lines                      17182    17474     +292     
=========================================================
+ Hits                       11215    11391     +176     
- Misses                      4360     4432      +72     
- Partials                    1607     1651      +44     

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