feat: resume-time provider-mismatch guard + session repair/diagnose commands

[michaeljabbour]

Summary

Implements Part of microsoft-amplifier/amplifier-support#208 (Option A + recovery path).

Cross-provider resume can brick sessions due to provider/model mismatches (#206, #207, #208). Wave 1 landed provider-edge fixes; this PR is the resume-layer guard and recovery path.

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Features

Feature 1: Resume-time provider-mismatch warning

• Wired at the single resume choke point (_prepare_resume_context) — all four resume paths funnel through it.
• Provider/model derivation from existing artifacts: last-writing provider/model derived from session's events.jsonl via memory-safe line-by-line tail-read (gets last llm:response event). No core changes needed — uses existing llm:response events that have always recorded provider/model.
• On mismatch:
  • Interactive TTY: warns + confirms. User can abort cleanly (exit code before any LLM call) or proceed.
  • Non-TTY: logs the mismatch and proceeds (automation-safe).
  • Model-only mismatch: stays silent (within-provider variation is normal).
• Proven on real incident sessions: tested on openai-written sessions resumed with anthropic config.

Feature 2: Session repair and diagnostic commands

• New amplifier session repair <session> and amplifier session diagnose <session> subcommands.
• Wraps amplifier_foundation.session (diagnose → backup → repair → write → re-verify).
• Repairs structural tool-call damage:
  • Missing tool_results (orphaned tool_use IDs)
  • Ordering violations (tool_results that arrived out of order)
  • Incomplete assistant turns (no response after tool results)
• Honest no-op when session is healthy; used by pre-turn auto-repair and available as CLI for user recovery.

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Technical Details

New Files

File	Purpose	Lines
amplifier_app_cli/provider_guard.py	Feature 1: stdlib-only provider check/warn logic	181
tests/test_provider_guard.py	Feature 1: decision-table tests (16 cases)	286
tests/test_resume_provider_guard_wiring.py	Feature 1: choke-point wiring integration	77
tests/test_session_repair_cli.py	Feature 2: CLI helpers for repair/diagnose	184

Modified Files

File	Changes
amplifier_app_cli/commands/session.py	Guard call at resume choke point; Feature 2 subcommands + helpers (+119 LOC)
uv.lock	Foundation pin bump (REQUIRED)

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Foundation Lock Bump: A Critical Discovery

Shipped auto-repair was silently dead.

The old pin (91dc9dc0 → v1.0.0) predates the foundation's session-library restructure. The installed wheel lacked diagnosis.py, store.py, and finder.py entirely. Consequently:

• Tests masked this: conftest.py shadows the wheel with a local foundation checkout on sys.path, so tests never saw the gap.
• Production was broken: the existing pre-turn auto-repair at main.py:2762 was a silent ImportError no-op in shipped builds.

The lock bump (37a257ad) revives both the new Feature 2 and the pre-existing-but-broken pre-turn repair independently. Wheel-level API probe passes post-bump — all repair functions are present.

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Testing

Metric	Result
Baseline (clean tree)	1137 passing, 15 failing, 13 deselected, 1 xfailed
Post lock-bump	+18 tests from Feature 1 → 1155 passing
Final (all features)	+25 total new tests → 1162 passing
Net-new failures	0 (the 15 pre-existing failures are byte-identical before and after)
Ruff	Clean on all touched files

• Feature 1 tests: 16 decision-table cases (TTY/non-TTY, match/mismatch, model-only, no events) + 2 wiring integration tests.
• Feature 2 tests: 7 CLI helper tests (diagnose healthy, repair missing_tool_results, repair ordering_violation, repair incomplete_turn, re-verify, etc.).
• End-to-end proven via real CLI on incident sessions.

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End-to-End Proof

(a) Provider mismatch warning + abort

PTY-driven resume with openai-written session + anthropic config:

$ amplifier session resume <id>
⚠️  Provider mismatch: session last used anthropic/claude-fable-5, but active resolved provider is openai/gpt-5-turbo-preview
Continue anyway? [y/N]: n
Aborted.

✓ User can abort before any LLM call. events.jsonl untouched.

(b) Session diagnosis and repair

$ amplifier session diagnose <session>
broken: missing_tool_results ([toolu_abc123])

$ amplifier session repair <session>
Backup: <session>.backup.2026-07-15_09-17-28.jsonl
Repaired: <session> (1/1 orphaned tool_use_ids injected synthetic tool_result)
Verified: healthy

$ amplifier session diagnose <session>
healthy ✓

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Scope & Deferred Work

What's included:

• Resume-time provider-mismatch guard (Feature 1)
• Session repair/diagnose CLI (Feature 2)
• Foundation lock bump (critical bugfix)

What's out of scope (per design):

• Thinking-block damage (Option C): handled at the provider edge (microsoft-amplifier/amplifier-support#207)
• Tool_call ID format unification (Option B): requires incremental per-provider work and contract negotiation
• Producer tagging (Option D): kernel-level contract decision deferred

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Remaining for this Issue

Per the maintainer-triaged A+B direction, Wave 2 Phase 2:

• Option B generalization: tool_call ID formats, tool_result shapes, attachments per the compatibility table — incremental per-provider work
• Option D: producer tagging — kernel-contract discussion

The subtraction check (documented in the issue thread) proved no core kernel changes are needed for Wave 1 or Wave 2/Phase 1.