Two related fixes from empirical testing of OpenCode's model
resolution against the controller's tier-escalation ladder.
ROOT-CAUSE FINDING (empirical, 2026-05-18)
==========================================
Spun up a probe agent (.opencode/agents/model-probe.md), asked the
model to self-identify, and tried three model-routing mechanisms:
1. **POST /session ``model`` in body**: OpenCode 0.x silently
IGNORES this — all probes returned ``openai/gpt-5.3-chat-latest``
(OpenCode's fallback default), not the requested haiku/sonnet/opus.
2. **.md frontmatter ``model:`` line** (after OpenCode restart):
HONORED — pinning to claude-haiku-4-5 yielded haiku, pinning to
sonnet yielded sonnet, etc.
3. **opencode.json ``agent.<name>.model``**: HONORED — same result
as .md frontmatter.
CONSEQUENCE: pre-batch-Q the tier variants had NO ``model:`` in
their .md frontmatter; the model lived only in
``.opencode/models/task-implementor-tier-<N>.txt`` files that the
dispatcher passed via POST /session body. Since OpenCode ignores
that pass-through, ALL FOUR tier variants ran on the SAME default
model (gpt-5.3 in this configuration) — the entire tier-escalation
ladder was cosmetic for model selection. The trial-2 sessions
logged ``model override -> claude-haiku-4-5`` but the actual
generation was on something else entirely.
WHAT THIS COMMIT DOES
=====================
1. **sync_tier_models.py rewrite** (already in batch P, refined here):
inject ``model: <providerID/modelID>`` line into each generated
tier variant's .md frontmatter. This is the mechanism OpenCode
actually reads at startup. The model values come from tiers.yaml
(source of truth).
2. **Drop the dead .opencode/models/task-implementor-tier-*.txt
files** (Option B): the dispatcher pass-through they fed was
empirically dead — OpenCode doesn't read the model from POST
/session. ``sync_tier_models.py`` now removes any stale .txt
files on each run (so a developer can't accidentally re-create
them).
3. **Test updates**:
- ``test_no_stale_variant_txt_files_remain``: pins that the .txt
files stay deleted (was ``test_every_tier_has_a_variant_txt``).
- ``test_each_variant_md_carries_correct_model_from_manifest``:
pins that the .md frontmatter model: matches tiers.yaml (was
``test_each_variant_txt_matches_manifest_model``).
- ``test_every_agent_file_reference_in_opencode_json_resolves``:
relaxed to skip when opencode.json has no agent block (which is
the Option B steady state). Still pins {file:...} resolution
for any future use.
- ``test_each_variant_md_matches_renderer_output_for_its_tier``:
updated to call the new renderer signature ``render_task_
implementer_variant(source, model)`` (was the byte-copy
identity test, retired because variants now differ by the
injected model: line).
- ``TestTaskImplementorVariantsAreByteIdentical`` → renamed
``test_variants_identical_except_for_model_line``: strips the
model: line via regex and asserts the rest is byte-identical.
OPERATOR WORKFLOW (unchanged surface)
=====================================
To swap a tier's model:
1. Edit ``.opencode/models/tiers.yaml`` (one line)
2. ``python3 tools/sync_tier_models.py`` (regenerates .md; removes
any stale .txt)
3. Commit both files
4. Restart OpenCode (it caches .md frontmatter at startup)
What's still ahead (deferred):
- ``_resolve_role_model()`` in tools/_opencode_worker.py is now
proven dead code (reads .txt files that don't exist; injects
model into POST /session body that OpenCode ignores). Should be
deleted in a follow-up — kept now to minimize blast radius.
- The misleading "if generation uses a different model, restart
OpenCode so opencode.json's {file:...} re-resolves" log line in
``_opencode_worker.py:1569`` is wrong post-Option-B; should be
retired with the dead code above.
- Whether opencode.json's agent block supports a ``permission`` field
is the gate for an even deeper simplification (Option D). Skipped
for now per operator direction; the controller path uses .md
frontmatter for permissions.
3148 tests pass, 4 skipped, 0 failures.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
drew
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