feat(debug): add eval-at probes

[pocky]

Summary

• Add tower_debug_eval_at, a stateless debug probe that launches a configured DAP program, captures breakpoint evidence, and tears down without exposing a persistent session.
• Extend the debug extension protocol, manifest, registry wiring, and docs so eval-at is advertised only when debug configuration is available.
• Cover hit, no-hit exit, timeout, DTO validation, manifest stability, and fixture behavior with focused contract and e2e tests.
• Clean up stale ZPM PR memory mounts from prior completed feature branches and record reusable F005 feedback rules.

Changes

Debug eval-at implementation

• extensions/debug/src/eval_at.rs: Add eval-at request/response DTOs, orchestration, bounded stack/local/arg capture, expression evaluation, timeout handling, cleanup, and unit coverage.
• extensions/debug/src/main.rs: Wire eval_at into debug sidecar dispatch and request handling.
• extensions/debug/src/protocol.rs: Add eval-at protocol support and typed error handling paths.
• extensions/debug/src/session.rs: Extend debug session behavior needed for one-shot probes, exited outcomes, output capture, and cleanup.
• extensions/debug/src/tools.rs: Register and dispatch the eval_at tool.
• extensions/debug/src/types.rs: Add shared debug result types used by eval-at capture and responses.
• extensions/debug/extension.toml: Advertise the eval_at tool with a strict JSON schema.

Protocol and engine integration

• crates/core_engine/tests/extension_debug_e2e.rs: Add merged-registry availability tests and fixture-backed e2e coverage for eval-at hit, no-hit exit, timeout, cleanup, and no session_id leakage.
• crates/extension_protocol/tests/protocol_tests.rs: Update debug manifest expectations from 12 to 13 tools and assert eval_at is present without workspace mutation capabilities.

Debug fixture support

• extensions/fixtures/debug_adapter/src/main.rs: Extend the fixture adapter with eval-at scenarios, output behavior, delayed continue handling, and no-hit exits.
• extensions/fixtures/debug_adapter/tests/eval_at_scenario.rs: Add fixture scenario tests for breakpoint hit, normal no-hit exit, and timeout-style behavior.

Documentation

• README.md: Update the debugging capability summary and docs index to include tower_debug_eval_at.
• docs/README.md: Add eval-at to the debug and MCP tool documentation index descriptions.
• docs/mcp-tools.md: Document tower_debug_eval_at arguments, response shape, finish states, timeout behavior, and condition handling.
• docs/user-guide/debug-sessions.md: Expand the guide from interactive sessions to sessions plus one-shot probes with example calls and responses.

Project memory

• .zpm/kb/feedback/journal.wal: Record F005 feedback rules for exact cargo test names, DAP timeout modeling, strict eval-at DTOs, and breakpoint ordering.
• .zpm/mounts.json: Remove stale PR memory mounts for completed F002 and F003 branches.
• .zpm/kb/pr_feature_f002_standalone_linter_sidecar_extension/journal.wal: Remove stale F002 PR memory segment.
• .zpm/kb/pr_feature_f002_standalone_linter_sidecar_extension/knowledge.pl: Remove stale F002 PR memory schema.
• .zpm/kb/pr_feature_f003_lint_fix_apply_machine_applicable_lin/journal.wal: Remove stale F003 PR memory segment.
• .zpm/kb/pr_feature_f003_lint_fix_apply_machine_applicable_lin/knowledge.pl: Remove stale F003 PR memory schema.

Test plan

• Run cargo fmt --check
• Run cargo clippy --workspace --all-targets -- -D warnings
• Run cargo build --workspace --bins
• Run cargo test --workspace

Closes #10

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